Formal:
* ¿Trabaja usted mañana? (Do you work tomorrow?) This is the most formal way to ask.
* ¿Tiene trabajo mañana? (Do you have work tomorrow?) This is another formal option.
Informal:
* ¿Trabajas mañana? (Do you work tomorrow?) This is a casual and friendly way to ask.
* ¿Vas a trabajar mañana? (Are you going to work tomorrow?) This is another informal option, slightly emphasizing the intention of working tomorrow.
You can choose the best option based on your relationship with the person you are speaking to.