。
What subject do you like studying?
Literal
Study [topic-は] what [subject-が] like (polite)?
A double-subject construction: 勉強は marks 'studies' as the overarching topic/frame, and 何が picks out the subject of the 好き predicate within that frame. This 'frame + embedded subject' pattern is characteristic of Japanese — literally 'as for studies, what is liked?' English collapses it into a single question.