This is the 8417th most frequent Korean word.
who가
"Who가" means "Who + subject marker (가)" in Korean, used to indicate "who" as the subject of a sentence.
This sentence uses 'who가' as a subject referring to an unknown person.
who가 누구인지 알고 싶어요.
I want to know who who is.
Here, 'who가' is used as the subject asking for the person responsible.
who가 이 집을 지었나요?
Did who build this house?
'누군가가' incorporates 'who가' (누구+가) in its indefinite form to indicate 'someone.'