The TL431 datasheet mentions that the VIKA is approximately 2 volts (when the input is more than Vref = 2.5 V), but based on my simulation, it shows me (1.07 V to 1.2 V). I need to know where I can find the VKA on-voltage based on the datasheet.
It's not specified and it's not important in most applications. It just has to be reliably well under 2.5V over process variation and temperature.
Looks like (from the datasheet) it has to be at least two diode drops based on the shunt transistor actually being a Darlington pair.
You can measure an actual sample, however it may vary somewhat between manufacturers and from unit-to-unit, so it's not really something you should depend on to an any degree of confidence. It will also certainly vary with temperature.
Just to indicate some differences- a simulation in LTspice with the 'TL431' model gives ~1.1V and a simulation with the TL431A model gives ~1.8V.