What is the difference between qua and qui in Italian?

You're likely thinking of the words "qual" and "chi" in Italian, not "qua" and "qui."

Qual and chi are both interrogative pronouns, meaning they are used to ask questions.

Qual (which, what) refers to things or concepts:

* Qual è il tuo nome? (What is your name?)

* Qual è la tua città preferita? (What is your favorite city?)

Chi (who) refers to people:

* Chi è quel ragazzo? (Who is that boy?)

* Chi hai incontrato oggi? (Who did you meet today?)

Let me know if you have any other questions!