How can I check which service is updating an attribute?

Each attribute can be updated by one service at a time. You can check which service is set to sync data for each of your attributes on your attributes page.

Exist attributes page showing the service for each attribute

If you have multiple services connected that can provide data for an attribute, you'll see a dropdown menu where you can change the service for that attribute. Otherwise, you'll just see the name of the service providing data for that attribute.