iPod Nano

If you have used the iTunes Restore procedure, you will now have to set Sync options for the iPod as though it was a new iPod. See this Apple article; Sync your iPhone, iPad, or iPod using your computer - Apple Support.

The article also has instructions to set up the iPod if you are using a newer Mac, with OS Catalina or later on it (as there is no iTunes for the newer Mac).

Try another Restore if the iPod itself is not responding.

If the iPod appears to be working, but doesn't show up in your iTunes, have a read of this Apple article: If your computer doesn't recognize your iPhone or iPad - Apple Support. If that doesn't help, try this tip from fellow user turingtest2: iOS device not showing in iTunes for Wind… - Apple Community

To set up iTunes to add music to your iPod:

• • Connect your iPod to your iTunes Library
  • click on the iPod icon that will appear at the top of the iTunes window:

• • this will display the Device/Settings/Summary pane
  • select the Device/Settings/Music pane (1.) as indicated below:

• • put the tick (check mark) in the box named Sync Music (2.)
  • for step 3, choose either:
    • Entire music library, which will add all your music and will not display section 4
    • Selected playlists, albums, artists and genres, which will display section 4. If you choose this option, you then select the items in section 4 that you want to add to your iPod
  • tap the Sync (or Apply) button in the lower right corner of iTunes (not shown in the screenshot)

It is unlikely that there is an update for your iPod nano.