it means "let me know that you are fine" or "let me know if you are alright" as they say above. also you can use:طمني عليك that's not standard Arabic. you are learning Egyptian Arabic,right?

Yaa it is true

yup, I think he means, how are you doing? let me know if you are alright? Is everything ok?

yaani if someone asks me this he is asking "how are you"

"Let me know that you are well (fine)."