To unlock the Audiophile trophy in Far Cry New Dawn, you will need to collect all 10 of the game's hidden MP3 players.
You can collect all of the MP3 players once you gain access to free roam. You will hear them when you are nearby, or you can wait until you upgrade the Cartography Station at Prosperity and buying the map from there.
You can find a video guide for each of the MP3 Player locations below (credit to Powerpyx for the video):