I am a teacher and was diagonsed with a hernia due to a work injury and was scheduled for surgery, My principal asked me what pain medication I was on in the main hall way of the school after findingout I had a work related hernia. Is this a violation? If so what recourse do I have.

How did the principal find out? Did he ask you in such a way that
Passersby could hear?

This is clearly a breach of ethics, but your only recourse would be to talk to your union rep. It is definitely not a criminal issue so I've moved your thread.