Who are Mitsuki's parents?
It has been revealed in Boruto: Naruto the Movie that, Mitsuki is Orochimaru's son.
Extract from the movie summary:

Boruto questions Mitsuki about his parentage, to which the latter says he is the son of Orochimaru. This shocks Sarada and she asks if Orochimaru is his mother or father while Boruto asks who Orochimaru is, and Mitsuki replies it doesn't matter, much to Boruto and Sarada's confusion.
source: Mitsuki