-(이)라면 puts a condition on who you are, and 알다 says that such a person knows the thing: 한국인이라면 아시죠? (if you're Korean, you know this, right?), K-POP 팬들이라면 아실 건데. Every line here is that shape, and it works as a nudge to the audience — naming an in-group and quietly flattering anyone who belongs to it.