Personally, I look for therapists for 2e/GT populations who have a nuanced and contextualized understanding of giftedness, and, if at all possible, evidence that they are GT themselves. And, obviously, professional competence in psychotherapy.
I would steer clear of sweeping generalizations about their GT clients ("all", "every one of my clients"), and disproportionate focus on narrow types of GT models (those who force everything through, say, a visual-spatial learner lens, or tag all behavioral concerns as mainly motor or emotional overexcitabilities). Along those lines, therapists that are oriented much more highly toward either the giftedness or the disability, rather than viewing a client holistically, in all of the complex, contradictory and intertwined glory of their 2e-ness, will likely miss the forest for the trees. You might be able to see this in how their professional writing and practice are distributed.
And another quality I'm not into in a therapist is arrogance. If we don't bring humility and humane curiosity to working with 2e learners, we won't be able to reach or help them. Anybody who says they know everything about 2e doesn't. A good therapist should be able to say, "I haven't necessarily worked with someone exactly like you (your son), but I can see some possible areas to explore that might connect to patterns I've seen in the past, of x nature." So, knowledgeable and confident, but not presumptuous or condescending.
...on another note, seeing your list of some of what your DC has been going through--whew! That is a lot! And with many possible interactions between physical/organic, neurobehavioral, and emotional concerns.
Wishing you the best for your call tomorrow!
