Any sound file that is used in the game. You said you knew where the folder was. Pick any. Search for its name.
Edit: For instance, I found EB_Easter_Greek_Battle_Theme.mp3 and searched for it in all the .txt files. And voila, it tells me that it's referenced in the descr_sounds_music.txt file. It's how I find everything in the mod which I haven't worked on before.
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