T's can ask, demand, whatever they think is best for you and your particular therapy situation. They generally aren't going to touch you or anything like that in the first place, not because it is a boundary or they're "not allowed" but because it's "talk" therapy. There are other types of therapy where touch is extremely appropriate and there are individuals who want literal hand holding, hugs, touching, etc. but if you do not want that they are probably going to ask first and you just say "no".

As far as seeing scars, etc. that would be an individual thing and you and your T would talk about it, etc. If your T thought looking at your scars was a good idea and you did not, you or your T might decide you needed to see someone else in therapy; deliberately hiding or not cooperating with a particular therapist's program would generally mean you and that therapist did not work well together and the therapist would probably not think they could help you so would suggest you see someone else or you'd decide you didn't like their "rules"/demands and decide to go see someone else, etc.