"Tu es toujours réveillé(e) ?"
* Tu - You
* es - are (conjugated form of the verb être, "to be", in the present tense, second person singular)
* toujours - still
* réveillé(e) - awake (masculine or feminine, depending on the person you are addressing)
You can also say:
"Tu ne dors pas encore ?" - "You're not sleeping yet?"
"Tu es toujours debout ?" - "You're still up?"
The choice depends on the context and the level of formality.