Should i create a new campaign or campaign group for my new domain?

Yes. If you have a new domain, we highly recommend creating a new campaign group as well as a new campaign. New domains can enter an auction for the same keyword as the old domain. Because of this reason, it is highly advised to create a new campaign group.

The only exception is when you are deprecating your old domain and replacing all old ads with new domain. Then you need not create a new campaign or campaign group. Just replace your old ads.