Get the Event Schema with REST API
To retrieve the event schema by schema ID, perform a GET request to this REST API resource and supply the schema ID: /services/data/vXX.X/event/eventSchema/schemaId. For more information, see Platform Event Schema by Schema ID in the REST API Developer Guide.
To retrieve the event schema by event name, perform a GET request to this REST API resource and supply the event name: /services/data/vXX.X/sobjects/eventName/eventSchema. For more information, see Platform Event Schema by Event Name in the REST API Developer Guide.
When the schema changes, for example, after an administrator adds a field to the platform event definition, the schema ID changes. You can determine if the schema changed by comparing the schema ID with the previous schema ID value.