They are stored in the application’s internal storage directory, not normally user-visible. Are you trying to play the offline downloads outside of the Pandora app? The offline music is stored in an encrypted format only usable by the Pandora app itself.
I haven’t used Pandora in a long time, but if it’s anything like Spotify, it’s encrypted so you can only play it back through the app. So if you have no service or are in offline mode, you can still “stream” the song, but you aren’t going to be able to find the MP3 file.
Ohh K. I found the offline mode in Pandora. I’ve a new car, and have paired the phone to it and just wanted to play downloaded songs. Makes sense that they just don’t give you .mp3’s or something.