It's a way of asking someone what's bothering them or why they're acting a certain way. It's a casual and informal expression.
Here are some examples:
* "Tu as quoi? Tu sembles triste." (What's wrong with you? You seem sad.)
* "Tu as quoi? Tu es tout rouge." (What's the matter? You're all red.)
Note: "Tu as quoi" is often used in situations where the person seems to be upset or experiencing some kind of discomfort.