Orgasm_Man: "What would you do to a very delicate sub?
How can you find out what she wants? "
That's one excellent question.

I been there with one partner, you ask and all replies was of the type 'what master wants'. And she did give extremely little input even in play, by just going limp whatever happened to her.

For me this turned into a crash course of learning to read her quite personal way of facial expressions when in play.

Yet more basic matters we found another approach, she's younger than me and the idea of cybering was a natural means of communication for her.
So we ended up with a sort of face to face and voice 'cybering'. I gave the input by desscribing a certain situation and she replied by giving the outcome: and I know it sound silly but it worked for us.
(Later on when she felt safe she went on to suggest some really outlandish things, which I ofc knew wasn't meant to be realized but was a really good mindfuck anyhow.)

So there's some pointers, but if everything fails in communication, send her the BDSM checklist and have her fill it in. You'd get some pointers from that one at least.