If you, like me, are wondering "has anyone just run it through a mass spectrometer to see what the ingredients are?" the answer is yes, they have.
I don't even drink soda.
If you're familiar with the taste of amaretto or marzipan, try thinking of those next time you drink a Dr. Pepper. That will unlock the flavor discrimination for you.
When I grew up, I tried Dr. Pepper, and immediately recognized the taste.