Notes
I have lost notes from my notebook.
How do i get them back?
See the article About using iCloud Notes on Mac - Apple Support
You can store notes in iCloud so that you can view and edit them on all your Apple devices, as well as iCloud.com. Notes stored in iCloud appear under iCloud in the sidebar of the Notes app. If you don’t see iCloud in the sidebar, you need to sign in to iCloud and turn on the Notes feature in iCloud settings. See Set up iCloud features on Mac.