It is not that simple. Not all trainers have a power meter. Bkool wheel-on has not (and I suspect most other wheel-on) but does some calculations based on roller speed and stuff and then outputs a watt-number to the computer, which may be more or less correct, depending on the alogithm. A real Power meter (in a trainer, pedals, crankarm, crankset) requires some sort of physical measuring device like a string gauge, an optical sensor etc. The same goes for cadence.
Speed is always calculated and will most likely be different on the computer and what is shown on the bike computer. Simulators like BKOOL, Zwift etc. calculates your speed using your poweroutput but also takes into account if you are drafting or not, road inclination, your weight, height etc. So you will probably never see the same speed and hence distance traveled. Speed outdoors is calculated from wheel-size (circumference) and number of rotations (requires speed/cadence sensor of course) or using the GPS in the bike computer.