Recover Notes from El Capitan in High Sierra My El Capitan machine unexpectedly died, and I salvaged the disk drive from it to put into an external enclosure attached to my new Mac, which runs High Sierra.  (I never used Sierra at all, since my old Mac couldn't support it.)

Now, how do I get the Notes from my El Capitan system into the High Sierra notes system?

(As I said, even though the old Mac threw-a-piston, I still have its drive, and therefore, all that notes-data.  But how do I get to it?)
Move old Notes (from your external drive) to iCloud

Drag and Drop

Allow it to sync (wait 5-10 minutes)

You should now see a duplicate Notes folders names (on your Mac (but not with exactly same content)

Those are the 2 Notes databases on iCloud

Now Select all Notes you want to keep and drag them over to new notes