Hi there,
There is no way to tell which flow sources are sending flows to which flow collectors (Polling Engines) unless you log in to each one of your flow sources and go through configs.
This issue has been discussed here: NTA - Sources per Engine
There should be an easier way. My suggestion is to improve the NetFlow Collector Services resource to include these details.
Here's how it would look:
The fields marked in orange are the fields that I have added.