"Do you want some?"
Translation:Tu en veux ?
- "T'en veux" is wrong. It is used in very informal speech, but not considered correct in written French.
- By comparing with "tu en veux?" you can see that the same structure using vous would be "vous en voulez?"
I believe another way of putting it would be "En voulez-vous?"
Edit I have been checking around, and "en voulez-vous?" can mean "do you want some?", but apparently it is also an expression with a general sort of meaning of blaming someone or resenting someone for something.
From Reverso: "M'en voulez-vous d'être curieux ?" = "Do you blame me for being curious?"