When you have a phone with Android Go, you can see it when you turn on the device. On startup screen with "Powered by Android" image, there should be also written "go edition".
Phones with Android Go have some Go edition apps installed instead of standard Android apps. For example on Android Go devices there should be Google Assistant Go, Google Go, Gmail Go, Google Maps Go, YouTube Go instead of regular Google Assistant, Google, Gmail, Google Maps, YouTube apps.
Android Go apps should have "GO" included in their icons.
Checking of Android version may depend on you device. On phones with recent Android versions, you can check the version in:
Settings > About Phone
Settings > System > Advanced > System Update