A family of Microsoft products that enable users to capture, organize, and reuse notes electronically.
It's not that easy without knowing the details.
There are two places where an admin has potentially access:
The OneNote cache
It exists only when a notebook is currently open in OneNote and needs detailed knowledge of the way how OneNote works.
The OneNote automatic local backup
This is the real danger because you can copy whole notebooks for foreign use from that location.
But you can prevent this by shutting off the backup feature in OneNote Options.
Bernd