Kyoungjoo, what you wrote is coloquial?
I thought it would be something like : 노래하라고?
(Literaly, "노래하라고?" means "You asked me to sing?")
But I'm not a native, so we need one to check (maybe Kyoungjoo could do it?:)
Otherwise, what about "노래할까?" (kind of "should I sing?")