In half these lines it means knowing beforehand how someone will react: 얘는 좋아할 거 알아요 "I know he's going to love this", 이거 말하면 싫어할 거 알지만 "I know saying this will annoy people", 안 볼 거 알죠 "you know they won't watch". The -ㄹ form makes it a prediction you are confident about, not a guess. The other half of these lines are a different thing that looks alike — ~할 거 아냐, a rhetorical "well, you'd have to, wouldn't you", built on 아니다 rather than 알다.