-ㄴ 거 packages a fact and 모르다 says someone does not know it. Three of these lines end in 몰라?, which is a jab rather than a real question: don't you know I'm the IT guy, don't you know crossing over is forbidden, don't you know upkeep matters. Used about yourself in the past it becomes a surprised admission — not knowing you had become middle-aged, not knowing a friend had retaken his exams.