I have all my notes on my Mac, and I want to move them to iCloud so I can use them on a different laptop. Using the image below as an example, how do I move all notes from "On My Mac" to "iCloud" so that they are stored on iCloud?
If you turn on iCloud after already creating notes in the Apple Notes app, those notes will be local to the device, and are not automatically added to iCloud.
To add local notes to iCloud manually you can select an item, and then move it to a new list by dragging the "Notes" folder under the "On My Mac" list to the iCloud list.
On macOS you may have a move all option as well.
in your image you have 126 Notes on icloud and 14 on your computer. To add notes to icloud just click the icloud link on the left and click on the 'add a note' icon to add new note.
You should backup you notes before doing this. There is an app called Note2Txt.app that will extract all your notes to individual text files. You can specify the folder to store the notes in and it runs quickly. You can store the folder with your notes in them anywhere you want.