ㄹ지 알다

know what to do or expect

Takes a question word plus -ㄹ지 and says whether you know the answer: 뭐 해야 할지 알지? "you know what we have to do, right?", 누나가 한 입 먹고 뭐라고 할지 알아요 "I know exactly what she'll say after one bite". Negated it becomes "there's no telling" — 어디로 튈지 알 수 없는 토크, a conversation you cannot predict, from the image of a ball bouncing off unpredictably. The -ㄹ form keeps it about something not yet settled.