Formal:
* Dormez-vous déjà? (Do you already sleep?)
Informal:
* Tu dors déjà? (Are you sleeping already?)
You can also use the phrase "Est-ce que tu dors déjà?" (Do you already sleep?) which is slightly more formal than "Tu dors déjà?".
Note: "Dors-tu déjà?" is grammatically correct, but it sounds a bit more formal than "Tu dors déjà?" and might not be as commonly used in everyday conversation.