As we ll have learned OneNote is missing from Office 2011 (or Office 365 for Mac). What's curious is that even current Microsoft Web Sites still indicate that OneNote is an available App for the Mac.
Go to this URL:
https://onedrive.live.com/about/en-us/apps-that-work-with-onedrive/
scroll down to "Popular Apps" then select "Mac" from the menu bar. You will see One Note is clearly listed as an available App for the Mac.