Here are the OneNote 2016 download links direct from Microsoft. Microsoft no longer includes OneNote as part of Office on the desktop, since it was replaced with the Windows Store (UWP) version, which is lacking many features. However, it’s still a free download – but don’t expect any additional development on it:
Click To Run versions (note x86 or x64 as needed):
http://www.onenote.com/download/win32/x86/en-us
http://www.onenote.com/download/win32/x64/en-us
You can also download OneNote 2016 (yes, 2016) from the Windows Store (this is not the UWP version)
Grab it while you can! And be sure to vote for the return of OneNote desktop here: https://onenote.uservoice.com/forums/327186-onenote-for-windows/suggestions/32737648-include-onenote-for-desktop-in-office-2019
