it isnt neccesary to use ´´nasıl´´

in common ; nasıl qualifies and asks adj

Turkish equivalent for "how well" is "ne kadar iyi":

how well do you dance? - ne kadar iyi dansedersin?

Nasıl? İyi danseder misin?

Question words can be used alone immidiatelly before a question to show:

1- a little extra curiosity (nasıl - how)

2- surprise, shock (ne - what)

Nasıl? İyi danseder misin? (curiosity) - How? Do you dance well? (to the best of my knowledge, in English, there is no this type of use of "how")

Ne??? Nasıl yapabildin bunu?(surprise/shock) - what??? How could you do that?

Maybe it is a bit clearer now.