뭘 할 건가

what will you do

→ 뭐+를
phrase Rare #24,446
what will you do A direct question about what someone plans or intends to do. The subject is usually understood from context.
KO: 주말에 뭘 할 건가?
EN: What will you do this weekend?

선물로 뭘 할 건가?

What are you going to give as a gift?

— 학이 난다 (1957)

그래서, 자네들 이 장소로 뭘 할 건가?

So, what are you guys planning to do with this place?

— 씨너스: 죄인들 (2025)

이제 뭘 할 건가?

What are you going to do now?

— 베를린 천사의 시 (1987)