Neither iTunes nor Finder* have a method to import from an iPod. However, since the only method for adding music to an iPod Classic is via iTunes, then your music should still be in the iTunes Library (your iTunes) that you used to add the music originally.
* New Macs do not have iTunes. Instead, use Finder to manage devices.
If you don't have your old library anymore, did you ever make a backup of your music? If so, use that to rebuild your library.
Another option is to use a third-party app to copy the music from the iPod onto your computer. This helpful article from fellow user turingtest2 offers much more information on this topic: Recover your iTunes library from your iPo… - Apple Community.
Finally, the remaining option is to rebuild your library by going back to your original source for each piece of music:
- for music purchase from the iTunes Store, sign into your Apple account (the same one that you used to buy the music originally) and re-download the songs
- for music purchased from online stores such as Amazon or Bandcamp, sign into your account with that store and download your past purchases from your account
- for music that you copied from CDs, re-copy from the CD
- for music from other sources (i.e. an artist website), go back to that site
Once you have either recovered or re-built your library, make and maintain a backup to prevent this loss happening again.