public class LookupReusableController {
    
    @AuraEnabled
    public static List < sObject > fetchLookUpValues(String searchKeyWord, String ObjectName) {
        system.debug('ObjectName-->' + ObjectName);
        String searchKey = searchKeyWord + '%';
        
        List < sObject > returnList = new List < sObject > ();
        
        // Create a Dynamic SOQL Query For Fetch Record List with LIMIT 5   
        String sQuery =  'select id, Name from ' +ObjectName + ' where Name LIKE: searchKey order by createdDate DESC limit 5';
        List < sObject > lstOfRecords = Database.query(sQuery);
        
        for (sObject obj: lstOfRecords) {
            returnList.add(obj);
        }
        return returnList;
    }
}

<aura:event type="COMPONENT" description="by this event we are pass the selected sObject(lookup list record) in the parent component">
    <aura:attribute name="recordByEvent" type="sObject"/>
</aura:event>

<aura:component implements="force:appHostable,flexipage:availableForAllPageTypes,flexipage:availableForRecordHome,force:hasRecordId,forceCommunity:availableForAllPageTypes,force:lightningQuickAction" access="global">
    <aura:attribute name="oRecord" type="sObject" />
    <aura:attribute name="IconName" type="string"/> 
    
    <!--Register the component level event-->
    <aura:registerEvent name="oSelectedRecordEvent" type="c:LookupReusable_Event"/>
    
    <li role="presentation" class="slds-listbox__item" onclick="{!c.selectRecord}">
        <span id="listbox-option-unique-id-01" class="slds-media slds-listbox__option slds-listbox__option_entity slds-listbox__option_has-meta" role="option">
            <span class="slds-media__figure">
                <span class="slds-icon_container" title="Description of icon when needed">
                    <lightning:icon iconName="{!v.IconName}" class="slds-icon slds-icon_small" size="small" alternativeText="icon"/>
                    <span class="slds-assistive-text">Description of icon</span>
                </span>
            </span>    
            <span class="slds-media__body">  
                <span class="slds-listbox__option-text slds-listbox__option-text_entity">{!v.oRecord.Name}</span>
            </span>
        </span>
    </li>
</aura:component>

({
    selectRecord : function(component, event, helper){      
        // get the selected record from list  
        var getSelectRecord = component.get("v.oRecord");
        // call the event   
        var compEvent = component.getEvent("oSelectedRecordEvent");
        // set the Selected sObject Record to the event attribute.  
        compEvent.setParams({"recordByEvent" : getSelectRecord });  
        // fire the event  
        compEvent.fire();
    },
})

<aura:component controller="LookupReusableController" implements="force:appHostable,flexipage:availableForAllPageTypes,flexipage:availableForRecordHome,force:hasRecordId,forceCommunity:availableForAllPageTypes,force:lightningQuickAction" access="global">
    <!--declare attributes--> 
    <aura:attribute name="selectedRecord" type="sObject" default="{}" description="Use,for store SELECTED sObject Record"/>
    <aura:attribute name="listOfSearchRecords" type="List" description="Use,for store the list of search records which returns from apex class"/>
    <aura:attribute name="SearchKeyWord" type="string"/>
    <aura:attribute name="objectAPIName" type="string" default=""/>
    <aura:attribute name="IconName" type="string" default=""/>
    <aura:attribute name="label" type="string" default=""/>
    <aura:attribute name="Message" type="String" default=""/>
    
    <!--declare events hendlers-->  
    <aura:handler name="oSelectedRecordEvent" event="c:LookupReusable_Event" action="{!c.handleComponentEvent}"/>
    
    
    <!-- https://www.lightningdesignsystem.com/components/lookups/ --> 
    
    <div onmouseleave="{!c.onblur}" aura:id="searchRes" class="slds-form-element slds-lookup slds-is-close" data-select="single">
        <label class="slds-form-element__label" for="lookup-348">{!v.label}</label>
        <!--This part is for display search bar for lookup-->  
        <div class="slds-form-element__control">
            
            <div class="slds-input-has-icon slds-input-has-icon--right">
                <!-- This markup is for when an record is selected -->
                <div aura:id="lookup-pill" class="slds-pill-container slds-hide">
                    <lightning:pill class="pillSize" label="{!v.selectedRecord.Name}" name="{!v.selectedRecord.Name}" onremove="{! c.clear }">
                        <aura:set attribute="media">
                            <lightning:icon iconName="{!v.IconName}" size="x-small" alternativeText="{!v.IconName}"/>
                        </aura:set>
                    </lightning:pill>
                </div>
                <div aura:id="lookupField" class="slds-show">
                    <lightning:icon class="slds-input__icon slds-show" iconName="utility:search" size="x-small" alternativeText="search"/>
                    <span class="slds-icon_container  slds-combobox__input-entity-icon" title="record">
                        <lightning:icon class="slds-icon slds-icon slds-icon_small slds-icon-text-default" iconName="{!v.IconName}" size="x-small" alternativeText="icon"/>
                        <span class="slds-assistive-text"></span>
                    </span>
                    <ui:inputText click="{!c.onfocus}" updateOn="keyup" keyup="{!c.keyPressController}" class="slds-lookup__search-input slds-input leftPaddingClass" value="{!v.SearchKeyWord}" placeholder="search.."/>
                </div>   
            </div>
        </div>
        <!--This part is for Display typehead lookup result List-->  
        <ul style="min-height:40px;margin-top:0px !important" class="slds-listbox slds-listbox_vertical slds-dropdown slds-dropdown_fluid slds-lookup__menu slds" role="listbox">
            <lightning:spinner class="slds-hide" variant="brand" size="small" aura:id="mySpinner"/>
            <center> {!v.Message}</center>
            <aura:iteration items="{!v.listOfSearchRecords}" var="singleRec">
                <c:LookupReusable_Child oRecord="{!singleRec}" IconName="{!v.IconName}"/>
            </aura:iteration>
        </ul>
    </div>
</aura:component>

({
    onfocus : function(component,event,helper){
        $A.util.addClass(component.find("mySpinner"), "slds-show");
        var forOpen = component.find("searchRes");
        $A.util.addClass(forOpen, 'slds-is-open');
        $A.util.removeClass(forOpen, 'slds-is-close');
        // Get Default 5 Records order by createdDate DESC  
        var getInputkeyWord = '';
        helper.searchHelper(component,event,getInputkeyWord);
    },
    onblur : function(component,event,helper){       
        component.set("v.listOfSearchRecords", null );
        var forclose = component.find("searchRes");
        $A.util.addClass(forclose, 'slds-is-close');
        $A.util.removeClass(forclose, 'slds-is-open');
    },
    keyPressController : function(component, event, helper) {
        // get the search Input keyword   
        var getInputkeyWord = component.get("v.SearchKeyWord");
        // check if getInputKeyWord size id more then 0 then open the lookup result List and 
        // call the helper 
        // else close the lookup result List part.   
        if( getInputkeyWord.length > 0 ){
            var forOpen = component.find("searchRes");
            $A.util.addClass(forOpen, 'slds-is-open');
            $A.util.removeClass(forOpen, 'slds-is-close');
            helper.searchHelper(component,event,getInputkeyWord);
        }
        else{  
            component.set("v.listOfSearchRecords", null ); 
            var forclose = component.find("searchRes");
            $A.util.addClass(forclose, 'slds-is-close');
            $A.util.removeClass(forclose, 'slds-is-open');
        }
    },
    
    // function for clear the Record Selaction 
    clear :function(component,event,heplper){
        var pillTarget = component.find("lookup-pill");
        var lookUpTarget = component.find("lookupField"); 
        
        $A.util.addClass(pillTarget, 'slds-hide');
        $A.util.removeClass(pillTarget, 'slds-show');
        
        $A.util.addClass(lookUpTarget, 'slds-show');
        $A.util.removeClass(lookUpTarget, 'slds-hide');
        
        component.set("v.SearchKeyWord",null);
        component.set("v.listOfSearchRecords", null );
        component.set("v.selectedRecord", {} );   
    },
    
    // This function call when the end User Select any record from the result list.   
    handleComponentEvent : function(component, event, helper) {
        // get the selected Account record from the COMPONETN event 	 
        var selectedAccountGetFromEvent = event.getParam("recordByEvent");
        component.set("v.selectedRecord" , selectedAccountGetFromEvent); 
        
        var forclose = component.find("lookup-pill");
        $A.util.addClass(forclose, 'slds-show');
        $A.util.removeClass(forclose, 'slds-hide');
        
        var forclose = component.find("searchRes");
        $A.util.addClass(forclose, 'slds-is-close');
        $A.util.removeClass(forclose, 'slds-is-open');
        
        var lookUpTarget = component.find("lookupField");
        $A.util.addClass(lookUpTarget, 'slds-hide');
        $A.util.removeClass(lookUpTarget, 'slds-show');  
        
    },
})

({
    searchHelper : function(component,event,getInputkeyWord) {
        // call the apex class method 
        var action = component.get("c.fetchLookUpValues");
        // set param to method  
        action.setParams({
            'searchKeyWord': getInputkeyWord,
            'ObjectName' : component.get("v.objectAPIName")
        });
        // set a callBack    
        action.setCallback(this, function(response) {
            $A.util.removeClass(component.find("mySpinner"), "slds-show");
            var state = response.getState();
            if (state === "SUCCESS") {
                var storeResponse = response.getReturnValue();
                // if storeResponse size is equal 0 ,display No Result Found... message on screen.                }
                if (storeResponse.length == 0) {
                    component.set("v.Message", 'No Result Found...');
                } else {
                    component.set("v.Message", '');
                }
                // set searchResult list with return value from server.
                component.set("v.listOfSearchRecords", storeResponse);
            }
            
        });
        // enqueue the Action  
        $A.enqueueAction(action);
        
    },
})

.THIS .leftPaddingClass {
    padding-left: 2rem;
}

.THIS .pillSize{
    width:100%;
}

<aura:application extends="force:slds">
    <!-- Create attribute to store lookup value as a sObject--> 
    <aura:attribute name="selectedLookUpRecord" type="sObject" default="{}"/>
    
    <c:LookupReusable_Parent objectAPIName="account" IconName="standard:account" selectedRecord="{!v.selectedLookUpRecord}" label="Account Name"/>
    <!-- here c: is org. namespace prefix-->
</aura:application>

public class LookupRelatedContactC {
    
    @AuraEnabled
    public static List<Contact> getCon(List<String> accId) {
        return [SELECT Id, Name, Phone FROM Contact WHERE AccountId=:accId];
    }
}

<aura:component controller="LookupRelatedContactC"
                implements="force:appHostable,flexipage:availableForAllPageTypes,flexipage:availableForRecordHome,force:hasRecordId,forceCommunity:availableForAllPageTypes,force:lightningQuickAction" access="global" >
    
    <aura:attribute name="selectedLookUpRecord" type="sObject" default="{}"/>
    <aura:attribute name="data" type="Object"/>
    <aura:attribute name="columns" type="List"/>
    
    <aura:handler name="change" value="{!v.selectedLookUpRecord}" action="{!c.selectedLookupChanged}"/> 
    <c:LookupReusable_Parent objectAPIName="account" IconName="standard:account" 
                             selectedRecord="{!v.selectedLookUpRecord}" 
                             label="Accounts"/>
    
    <br/><br/>
    
    <lightning:datatable columns="{! v.columns }"
                         data="{! v.data }"
                         keyField="id"
                         hideCheckboxColumn="true"/>
</aura:component>

({ 
    selectedLookupChanged:function(component, event, helper) { 
        
        component.set('v.columns', [
            {label: 'Contact Name', fieldName: 'Name', editable: true, type: 'text'},
            {label: 'Phone', fieldName: 'Phone', type: 'phone'}
        ]);
        
        var aId = component.get("v.selectedLookUpRecord").Id;
        
        var action=component.get('c.getCon');
        action.setParams({accId : aId});
        action.setCallback(this, function(response){
            var state = response.getState();
            if (state === "SUCCESS") {
                var rows1 = response.getReturnValue();
                console.log('rows1 ->> ' + rows1);
                component.set("v.data", rows1);
            }
        });
        $A.enqueueAction(action);
    } 
})

<aura:application extends="force:slds">
    <c:LookupRelatedContact/>
</aura:application>