I have an old Ubuntu machine that no longer works, but I can still access its drive through a live USB. None of the notes were ever exported; though, I was expecting to recover them by some other means. How do I do this? I see the Joplin app folder/files and that it was installed on the machine via snap.
Those are stored in an SQLite database. Default location (normal and snap):
Find the one you are after on your system and then from command line you can do ...
sqlite3 ~/.config/joplin-desktop/database.sqlite sqlite3 ~/snap/joplin-desktop/current/.config/joplin-desktop
and then use the SQL language to view and dump data from it.
.help will show available options.