How much socialization with other dogs does my adult German Shepherd need?

Dogs don't need socialization with dogs from outside their circle of family/friends. As long as you are meeting your dog's needs for exercise, training, and enrichment - meeting or saying hi to other dogs isn't something necessary and in some cases, it's detrimental to a certain type of dog. I do want my dogs to be neutral around unfamiliar dogs and people but I never allow them to meet and interact with dogs I don't know. Too many chances for an issue.

Here is part of a lecture from one of our puppy courses but it applies to adult dogs in reference to socialization... Early Stages of Socializing with Michael Ellis Part 1

I hope this helps.