The best way to see notes for Program Event registrations would be through a Registrants query: 
  1. Go to Analysis>Information Library and click Add an Ad-hoc query. Select the Registrants source view.
  2. Click Program Event in the left column, and drag Event Record from the Middle column to Include Records Where. Set it to the proper Program Event.
  3. In the left column, click Registrants at the very top of the Left column, and drag Notes from the middle column to Results Fields to Display.