Roger,
You can use a retrieve by association action in a microflow or nanoflow to get data from a non-persistable entity. One thing to keep in mind: objects in non-persistable entities are only available in the current state and you will lose access to them if they are not associated to something in your current state (you can read about state here: https://docs.mendix.com/refguide/monitoring-client-state#1-introduction). So you can’t, for instance, perform a general search for all exisiting objects in a non-persistable entity.
Hope that helps,
Mike