nygaardgoes Is there an somewhat simple way to see it?
No, no simple way. You can turn your computer into a Wifi hotspot and run Wireshark on it to capture all network traffic your phone generates, while you use various apps, but it requires a lot of knowledge into how networking works to be able to read out anything useful from such a capture. I heard some people put a DNS logger of some kind in the VPN slot, which might give some information too, while being far easier to read and understand, but also not near as complete.
I guess an app might need to declare somewhere too what intents it can call, or that it exports for other apps to call, which might give you some insight into what apps communicate with other apps. But I don't really know how this works, so that is just speculations.
But it would have been really neat if GrapheneOS would log all called intents and contacted network hosts, and would display this in the Settings somewhere, per app. I think it would make many of GrapheneOS' target audiences feel more at ease.