To be very clear upfront: Not all shelter dogs have a trauma and need special attention. It is rather rare (violent prior owner, dog-dog issue in the shelter or at prior owner, multiple relocations, prolonged shelter residence, and such things). Feeding kibble does not lead to a trauma (surprise) - only to dog health, dog care, and dog behavior problems. The same is true for lack of exercise for a German Shepherd Dog.
Nonetheless, some shelter dogs do have a trauma (and some non-shelter dogs too!), and it's good to be prepared when you adopt a rescue German Shepherd. Not to make this quick "decision tree" suffer crush load, but in ultra short:
How to notice a dog trauma
Firstly, a trauma can result in a tremor, a spasm, or a twitch, thus these bodily signs may be an indicator for an existing trauma (both a bodily trauma and an emotional trauma, but here we only consider emotional trauma). Most dog owners however will only notice a trauma from unexpected behavioral signs, say the dog trembles or ducks away or hides when you raise your arm, or undress, or bring out the leash, or whatever.
Yet, a dog trauma can also show as more mundane behavior such as aggressive barking or fearful retreat barking upon meeting another person (often male) or another dog (irrelevant of gender and size). Even dog biting in certain situations, and only those, can indicate a dog trauma. While other so-called "dog behavior problems" such as whining, digging, jumping up, excessive attention-seeking, scavenging, chewing, chasing something etc normally have nothing to do with a trauma, they all are caused by insufficient socialization and inadequate training!
How to treat a traumatized dog
When you notice a trauma of your adopted rescue dog (see 1), first gain confidence that your interpretation of your observation is correct (that your dog really has a trauma), by recording in what situations and environments your dog shows the particular behavior (in writing, and ideally filming it too). Only if your records show that your dog consistently shows the trauma indicators that you are concerned about, then it will be a dog trauma - else it may be a tic or even a (consciously or unconsciously!) trained behavioral remnant from a prior owner or handler.
Then when you are confident about your dog's trauma, consider it in your own behavior and behavioral responses towards your dog: For example, if the trauma manifests as ducking away when you bring out the leash, then initially have the leash permanently lying on the floor near the door, make slow movements, and no surprise movements. Let your rescue dog anticipate everything you do. If there are no surprises, this kind of trauma will disappear without further ado.
How to avoid a dog trauma
The following relates to all dogs, not only to rescue dogs, whether still in a shelter or now with you as latest adopter. To avoid that a dog ever suffers a trauma: Don't use excessive Obedience Training (mark that Obedience Training is only used and promoted by people who haven't yet woken up to Behavior Training, which is superior in every regard). Don't startle a dog (in nature only a predator would startle a dog). Don't use force (whether the entirely useless/needless electronic shock collar or physical punishment), brief isolation works so much better! Avoid shouting at a dog. Don't leave a dog alone for a period longer than (s)he can routinely hold bladder and bowel. Always provide sufficient water to a dog. Don't strangle a dog at the neck with a prong collar, martingale collar and the like, simple leash training works so much better!
Simple, obvious things like these, that's it. Treating a dog well doesn't require a science degree, nor does it require a professional dog trainer (although they like to make us believe it does). It does require natural homemade foods, but that's a different topic on a different page.
Note that every key point raised above you can find more comprehensively explained in other places on this website. The menu is your friend. Here, links have been omitted only to keep this decision tree straightforward.
PLEASE NOTE: Posting a fragment of your overall dog problem in the comments below is not going to help. Provide complete details if you really seek the right solution. Of course we have a page for that as well: Dog Problem Consultation.