Informally, people would say, in North America, "What time do you get off work today?" or "When do you finish work today?" "What time do you have to be at work today?" or "What time do you start work today?" "Do you have to go to work today, even though it's the weekend?" You might also ask "When does your job start/finish today?" but this has a slight implication of meaning a non-professional job, or one where you are paid by the hour. There are other ways to ask these questions too, but these are very common.