API: write/read another user's notebook
If another user has shared a notebook with me, the API should expose this and make it available for editing (or reading, if read only).
This would make for some very interesting social options.
To be really useful It would require each user having the ability to specify a default notebook away from the API, i.e. at the OneDrive level. So if I were - say - writing a note that I wanted to 'send to Joe Blogs' that page would appear in their default notebook, not $Username's notebook, which they may not even have open.
Dipak Boyed (OneNote API team lead) commented
This should already be supported today. When you GET a list of notebooks, it will include those shared with you by others and if the UserRole is contributor, then you can create/edit pages under the shared notebook.