The compatibility of iPods is varied, able to play audio files in the format of AAC, MP3, PCM, Apple Lossless, FLAC, and Dolby Digital. However, all music from Spotify is streaming content protected by digital rights management so Spotify music is only available within Spotify itself. That’s why you cannot listen to Spotify music from iPod.
If you want to reach Spotify music to iPod, the best choice is to remove the private content copyright from Spotify and convert Spotify music to iPod supported audio formats. How to do this? To achieve it, you may need Tunelf Spotify Music Converter for iPod. Then you can download Spotify music to an iPod for listening.