If you're only talking about today, I think 'Is it your day off today?' would sound natural. Or in other ways and if you're talking generally, you could also say: Are you going to have a day off? Do you have a day off?

I would say 'Is it your day off?' or 'do you have a day off?' are the most natural ways to ask about this topic. Hope this helps!

Hi Ko Go,. We usually say "do you have the day off today?". Or "do you have off today?" Or "is today your day off?". As they are more common. However, "do you have a day off today?" Is ok but not as grammatically correct. Hope this helps.