Welcome to the Apple Support Communities. I understand you're having some trouble with one of the speakers on your iPhone, and I'd be happy to help you figure out why that is. To answer your question, there are two speakers built into the iPhone X: one stereo speaker at the base, and one next to the front-facing camera at the top. Check out the 'External Buttons and Connectors' section of this page: iPhone X - Technical Specifications - Apple
Also, you didn't mention which software version is currently installed on the iPhone, so head to Settings > General > Software Update and make sure it's the most current. If it isn't, back up your iPhone beforehand, then go ahead and update the software: Update your iPhone, iPad, or iPod touch - Apple Support
Lastly, be sure to try different combinations of songs and music sources for testing purposes, because in some cases that specific upload of a song or the song itself might use single audio channels as part of the track. Be sure to update the thread after you've been able to give these steps a shot, that way we can keep working towards next steps if need be.