These sentences are quite tricky to translate, but I tried my best not to distort the original message, keeping translation as close as possible to their literal meaning.
날 사랑하는 만큼 말해봐. => Tell me how much you love me (Verbally express how much you love me.)
~ㄴ 만큼 : as much/many as ----> 날 사랑하는 만큼: As much as you love me
말해봐 : Tell (me) / Speak
cf. ~해봥: A cute, informal expression of "~해봐". Commonly used in chatting
언니 말해 뭐해요, 말해야 알아요? => Why bother saying it? Do you know it when I only speak it out?
( Why would you want me to explicitly speak it out? You know that I love you even without a word.)
언니: An intimate/friendly way to call a female friend/sister who is older than the speaker.
~해 뭐해(요)? : What is the point of doing ~? / Why bother doing ~?
I hope it helps!