Two One Drive Accounts - Can I merge or copy?

Hi Marie,

From your description, we would like to convey that merging the content of two OneDrive account is not possible but however you can copy the content from OneDrive account to another OneDrive account by syncing the both OneDrive account to your PC and select the content to copy and paste it to another OneDrive account.

Note: We can't merge the two OneDrive accounts because we can't merge two Office 365 accounts.

You can refer to this article: Sync files with OneDrive in Windows to setup the OneDrive account on your PC.

But for copying the Notebooks to another OneDrive account, you need to follow the below steps:

1.Open the notebooks from OneDrive (from where you want to move) in OneNote 2016 for Windows application. 
2.Click File>Export>Notebook>OneNote package>choose a local drive path (e.g. Desktop).
3. Double click the notebook package on the Desktop. We will get a pop-up for un-packaging the notebook. Now you will get a new folder for this notebook.
Note: Do not choose the OneDrive for Business synced folder as a path. You may still choose Desktop or other local folders.
4. Open the Open Notebook in the un-packaged folder with OneNote desktop application or the folder you selected during the unpacking.
5. Click File>Share>choose another OneDrive for Business library>Move.

Note: You can click Add a place>enter your school account to add your OneDrive for Business library as a path.

You can also use the Microsoft Flow to move the content between to OneDrive accounts, you can refer to this article:

Copy files from one OneDrive account or folder to another.

Please let us know if you have any queries. Appreciate your understanding.

Regards,
Chitrahaas