DISCLAIMER:
Potterworld or Droobledore LLC is not in any way affiliated with Mojang AB, J.K. Rowling, Warner
Brothers or any company, copyright or trademark.
There's no specific number of subjects since occasionally new subjects are created by professors to be taught, but generally the most common ones include duelling, potions, charms, defence against the dark arts, creative writing, flying, history of magic, and more. You can click the calendar section of the website found between forums and games and see the current classes being taught on the schedule.