Background/Overview
The version of OneNote that you are using could determine whether or not your notebooks will migrate without any additional work on your part.
OneNote for Windows 10

If you are using OneNote for Windows 10, your notebooks are not stored in OneDrive and will NOT be migrated with the rest of your files.
OneNote for Enterprise or Office Online

If you use OneNote for Enterprise or the Office online version, your notebooks are stored in OneDrive and WILL migrate with the rest of your files.
How do I know if my notebooks will migrate?
As stated above, if your notebooks are stored in OneDrive, they will be migrated with the rest of your OneDrive content. If you have not yet migrated, you can look in OneDrive to see if your notebooks are stored there.
1. Go to https://www.microsoft365.com and log in.
2. Open OneDrive.

3. Click My Files on the left.
4. Click on OneNote notebooks.

5. The OneNote notebooks listed here will all be migrated with the rest of your OneDrive content.
How do I move a notebook to OneDrive so it will migrate?
1. Open File Explorer (on Windows) or Finder (on Mac).

2. Navigate to your OneNote Notebook folder. Select the notebook you wish to move.
3. Press CTRL + X (Windows) or Command + X (Mac) to Cut the folder.

4. In File Explorer or Finder, navigate to your OneDrive folder and then click your OneNote notebooks folder.
5. Press CTRL + V (Windows) or Command + V (Mac) to paste the notebook folder into the OneDrive folder.

6. The notebook folder you cut should be pasted into the OneNote notebooks folder.

7. Open OneDrive on the web and navigate to your OneNote notebooks folder.

8. Click the notebook to open it. If you get an error that the content cannot be displayed, wait a minute for it to resolve.
I am getting an error that my notebook isn't synching. What do I do?

If you see the above error, make sure you are opening your notebook from the OneDrive folder.
1. Click the drop-down list of notebooks in OneNote.

2. Right click the one that's not synching and choose Close This Notebook.
3. Click File > Open.

4. Click OneDrive in the list of locations and then choose the OneNote notebooks folder on the right.

5. Click the Open Notebook.onetoc2 file.
6. Your notebook should open and sync correctly.