What do you suggest if my mom wants me to wear diapers on a long car trip?

Your age: is not clear here, I am assuming you are not 47 years old. If you are old enough to answer this question and you have no problem with normal bladder function then it is not an appropriate request. Ask your mother why she is making this request. If she does not have a good reason, I suggest you discuss this with a trusted and responsible adult.