To me that looks like a more general doubt than to specifically play audio on a 3DS. Can you already code a program to play an .ogg file on your computer?
Since the 3DS has it's own system, access to the DSP is probably different to computer's in general, so you would probably need to send the audio data through some way to
devkitpro. But since I never coded on consoles, I have no idea how the system works and how it's made, so maybe I'm just throwing random statements without knowing if they are true or false, regarding the 3DS.
Nevertheless, if your problem is more general like "how to I make an app that reproduces audio", take a look at the
audio output method from a project I'm working on with some friends
(starting from line 51). We use PortAudio to give us access to the sound card, and libsndfile to read codified sound formats. From there it's just a matter of outputting audio samples to a buffer that gets sent to the sound card for playback.