Iris:
Left pane (Settings) -> (Network)
You can see the relays you use here. You can add and remove relays.
I don't use Iris, so I have no idea on how to see other peoples relays there.
In https://coracle.social client, you can see the relays a user is using in his profile.
Sorry for the broken link, I wanted to show you this:

primal not even the whole message is visible..