가 뭘

what …?

→ 가
phrase Very common #1,099
what …? 가 marks the subject, and 뭘 is a shortened form of 무엇을, meaning “what” as the object. The rest of the sentence determines the full English translation.
KO: 민지가 뭘 찾고 있어요?
EN: What is Minji looking for?

무함마드가 뭘?

What about Muhammad?

— 똑바로 살아라 (1989)

어니가 뭘 갖고 싶어 할지 알아봐.

Find out what Ernie wants.

마리아가 뭘 한단 말 인가?

What did Maria do?

— 희생 (1986)