There is provided mechanisms for discovering, for data collection, which NEF or AF is serving a UE. A method is performed by an NWDAF entity. The method includes providing, to a 5GC network function entity, a query of which NEF or AF is serving the UE. The method includes receiving, from the 5GC network function entity, a response comprising an ID of the NEF or the AF when there is a NEF or AF instance stored in the 5GC network function entity for the UE.