Sculpting Clothes is about drapery, how the folds interact etc. Try reading some good books about the subject, there are some good ones by Cliff Young, Michael Hampton, Burne Hogarth etc, they go through how gravity and forces interact with the folds to create the forms you see.
Wrinkles is kinda similar, how gravity affects the wrinkles etc, where they occur and why. But this changes depending on what your sculpting. However skin in general really does act in a similar way so generally you tend to see the same kind of wrinkle structures in most animals. I find working the wrinkles up slowly layer by layer is a good way to get a better sense of depth when working with wrinkles.
I use the slash brush (you can also use dam standard) to do wrinkles generally.
The Sphinx cat is looking great. Try the atlas of animal anatomy for artists to see the anatomy of the cat and if you have the forms correct.