Users are able to classify, label and protect Onenote Notebooks and section with Microsoft Information Protection sensitivity labels
Word, PowerPoint, Excel and several third party applications support MIP labels to flag the sensitivity and confidentiality of a document, apply protection and enforce display of content markings.
OneNote Notebooks include just as much sensitive information documents do, and users should be able to label them in the same way with a consistent user experience.
Ted Hacker commented
at the least mark a notebook with MIP classification AND apply encryption protection. It would be AWESOME to also apply MIP to a OneNote section
Rob Quickenden commented
This would be very good for onenote