Yes, it is a correct sentence. We use the present simple to talk about things that happen regularly and usually. So if it is the weekend or evening, and you are talking to a young person who is wearing normal clothes at the moment (jeans, t-shirt, whatever) and you say 'Do you wear school uniform?' you mean 'Do you wear school uniform (.....when you go to school)?', so the use of the present simple is correct. However, if you see a boy wearing a jacket and tie etc, and you want to know if these clothes are his school uniform, then you would say 'Are you wearing a school uniform?' . This means 'Are you wearing a school uniform (at the moment)?' As with everything to do with language, it depends on the situation.