There are tons of Dobermans boards and groups out there on various sources.  Some of the yahoo ones are very good, depending on what you're looking for.  healthdobes is good, imo.  Some of the rescue ones are for their own adopters/volunteers only.  Some are for specific clubs and their members only.  Some are for specific breeders and their owners only.  Some are archives only.  Some are largely inactive.  Some are kind limited in their focus and might not serve your particular interest.  All you can do is try to sign up for what you think interests you and see ...  If it doesn't work for you, unsubscribe.