I built an RC oscillator, chained it with an op-amp, and used it to drive a speaker. Then I cranked it up to the 20 kHz range. So I can tell you that I can hear above 22 kHz. We did "double-blind tests" where someone else was turning the sound on and off. I could always tell.
Some people can hear it, some people can't. Unfortunately, the "can't" people designed the Red Book audio format, apparently. I forget the exact frequency at which it became inaudible.
P.S. A lot of people have hearing damage because they listen to music at a volume which is too loud. You need earplugs at most concerts to avoid this.