는 분 알다

as those who know will know

분 is the polite word for a person, so 아시는 분 is 'those who know' and 보시는 분 'those who watch'. All four lines here are the same stock phrase to an audience — 아시는 분 아시지만, 'as some of you already know' — which flags background the speaker will not stop to explain. It is a way of including the informed without boring them.

Register: addressing an audience, polite