Lately during my high jumps my leg/knee has kind of been collapsing and this even happened to me dunking a basketball the other day. My approach is not that fast and I am under control, I don’t think there is excessive breaking going on. Is this a factor or weakness in my quads or a CNS thing?

Hard to say, but if it collapses inward, you might want to look to the glute medius. Other possible causes, but thats the first thing I would look at. Search around for info.

Yes - check your hips (glutes) and see if there is a problem with regard to lack of recruitment/firing.

Agreed with N2,it could be a general feedback problem,limiting your turning on ability. Check ankles and feedback from the feet related structures as well.