Yap.Town

뭔지는

what it is

→ 뭐+인지+는
뭔 what + 지 Clause-ending marker for assertion or confirmation + 는 Topic marker
pronoun Rare #26,054
what it is 는 marks this phrase as the topic, often with a contrastive sense.
KO: 그게 뭔지는 아직 몰라요.
EN: I don't know what it is yet.

산이 뭔지는 나도 몰랐다.

I didn’t know what an acid was either.