ConnectApi.ReadByCapability

If a feed element has this capability, the context user can mark it as read.

Property Name	Type	Description	Available Version
`isReadByMe`	Boolean	Specifies whether the feed element has been read (`true`) or not (`false`) by the context user.	40.0
`lastReadDateByMe`	Datetime	Last date when the feed element was marked read for the context user in ISO 8601 format. Otherwise, `null`.	40.0
`page`	`ConnectApi.ReadByPage`	First page of information about who read the feed element and when.	40.0

Apex Reference Guide