Is there a way to view the notes pane when grading a student PPT submission without having to download the presentation?
Unfortunately, there is not a way to view the notes pane when viewing a Powerpoint file in Canvas. In order to view the notes pane you would have to download it outside of Canvas and open it up on your device. The docviewer has a few limitations when it comes to displaying files such as Powerpoints. This appears to be one of the limitations. I apologize for the inconvenience on that.
HERE is the Canvas guide for what the Doc Viewer can display.