You probably mean what the employer can ask.
I am pretty sure, that you do not have give your doctors name or the nature of your visit. WE ARE NOT IN RUSSIA OR IRAN.
I am at a point at work, that I don't even tell my boss, why I have to have the day off, I need it off, PERIOD. But my boss is
really nice and if he would ask, if it was important, I would tell him that I have a doctors appointment.
Tell him, that you have a doctors appointment and that's it.
Honey, don't take crap from anybody.
I may have been dealt a bad hand, but at least I'm still playing with a full deck. ( most of the time anyway).