How do you know what you are?

Are there multiple protocols to figure it out, like FTP or a single accepted truth out there?

There are multiple ways to arrive at CdA.
Programs like Best Bike Split will give you a figure based on a recorded ride, a wind tunnel session or some variation of Virtual Elevation testing whether a paid session in a velodrome or your own testing using something like the calculator in Golden Cheetah.
There’s a thread called The Platypus Thread on ST with tons of info on VE testing including the guy who invented it Robert Chung.
Ps. From what I’ve read so far none of those new devices you bolt to your bike are there yet, without a lot of additional calculation similar to VE testing.