You can review the Capabilities metadata document to discover if an action supports asynchronous requests:
https://sam.spclouddave.com/SampleService/Sppid/V3/Capabilities/$metadata
In the SampleService, the RetrieveGdsUri action does not support asynchronous requests while PrepareViewableObject does.
See Reports (OData+) or Parametric Filters (OData+) for examples of asynchronous execution.