Neither. It is held in a database replicated on every Sonos device. Why do you care?

The Sonos app does not provide me a file path to the song/file. I am trying to retrieve the path to a bunch of songs as I have lots of duplicate songs/files on the file system. 

I’m not sure I understand the issue. You’ve already told Sonos where to get the data from, can’t you just search that location for duplicates, and after you’ve cleared them up, re-run the Sonos process to update your library?

I’ll take it as a “No”

Once you have sorted your original music library at the designated UNC path, you just simply re-run the indexer in the Sonos App ‘Settings/System/Music Library’ (Update Music Index Now etc.) - You can either do that manually, or by daily schedule …and the changes you make to your library will then be updated for the Sonos sysyem once the library index has completed. This is reflected in the database held on each of your Sonos speakers as mentioned earlier.

Note: You can add more than one library path if you have several local music libraries stored separately on PC HDD’s, NAS boxes etc.