Q. Can we make dua while in a state of sajdah during any prayer (farz, sunnah, witr, nafl prayer)?
A. Yes, it is permissible to make dua in Nafl Salaah in the Sajda posture. However, your dua will have to be made in Arabic seeing that you are in Salaah.
If you wish to make your duas in another language (besides Arabic) then you can raise your hands and make dua (as is normally done) or you can go into the Sajdah posture (when you are not in Salaah) and make your duas.
And Allah knows best.
Mufti Waseem Khan