I decided to have a tattoo, please help me to translate this phrases, thank you so much.
Memento qui sis.
I took "who you are" as something more like "what kind of person you are".
"Memento quis es" — that "es" should be "sis" in classical Latin. However either way this literally means "remember who you are" as in remembering what your name is, etc. – literally who you are. However I suspect what you want is more what kind of person you are.
"Memento qui tu es" — again the "es" should be "sis" in classical Latin. The "tu" is fine but unnecessary.
I would recommend "memento qui sis".