Pretty sure the knight captain is actually the emperor, we didn't see him rise like the rest of the fallen soldiers, only bloodied on the ground. as for the thing she used to verify she had the right target, it could be just matching the test sample to a previously collected one. The real emperor could be using a body double at all times that was trained to respond as the emperor wishes and the sample could be taken from the double. Just guessing on all of this though.