What is three surprising things that Percy discovers through his conversation with Mr. D and Chiron.

My answer is being made while assuming that you mean the consversation at the beggining of the percy jackson series.

1. Percy discovers that gods are real.

2. Percy discovers that Chiron, who Percy though was a normal teacher, is actually  half-horse half-man.

3. Percy discovers that Camp Half-blood is a camp for demi-gods such as himself.