Banned domains aren't always listing, some domains are replaced with random garbage.
Otherwise, this information should probably be on the wiki somewhere. When banned domains were first introduced, the information was listed under the deity. But for some reason that was removed at some point. The system has since expanded, and is a nasty surprise mechanic. I've had a few instances where people will tell me their cleric plans, and I'll tell them the domain they want to take is banned for their deity.