Formal:
* Que feriez-vous avec un béret? (This is the most grammatically correct and formal option.)
Informal:
* Qu'est-ce que tu ferais avec un béret? (This is a more casual way of saying it, using the familiar "tu" instead of the formal "vous.")
* Tu ferais quoi avec un béret? (This is even more informal, using the familiar "tu" and a more colloquial phrasing.)
Additional Considerations:
* Context matters. If you're talking about a specific type of beret (like a Basque beret), you can specify it in the question: "Que feriez-vous avec un béret basque?"
* Adding more details: You could also add more details to your question, such as "What would you do with a beret if you were in France?"
Let me know if you have any other questions!