Jon decided to use the stone to find out why it didn't work on Mr. Reynolds. "I wish to know why my last wish didn't work."
After the stone glowed, Jon knew. And he was shocked at the answer.
The stone wouldn't work on Mr. Reynolds because he has been protected from the stone's magic. Jon wished to know how he was protected, but the stone wouldn't tell him.
Jon thought that maybe he should find out a little more about his history teacher. The stone was obviously useless when trying to find out information about Mr. Reynolds, so Jon had to find out some other way.
This was more than curiosity. If the stone couldn't be used on him, then he could be a danger to Jon. And who knew if there were others who weren't affected by the stone, as well.
