-고

누구고? asks who a person is. 몇 시고? asks what time it is. These are bare present copular information questions, paired with yes/no -가. With past-tense material, use -노 instead: 어느 학교 학생이었노?.

Do not confuse this sentence-final ending with the ordinary connective -고 meaning and/then. The question word, predicate and final position identify this use.

The familiar register matters. In a formal interaction, use an appropriate polite question rather than attaching this regional ending to a polite stem.