Suppose there are twin brothers, one which always tells the truth and one which always lies. (So in this case they both know what is true and false, or as you put it, both are accurate in their knowledge.) What one yes-no question could you ask to either one of the brothers to figure out which one he is?
The question one could ask is: If I were to ask your brother whether you always tell the truth, what would he say?
A reply of “no” means you are talking to the truth teller, a reply of “yes” means you are talking to the liar.
Another possible question is: If I were to ask you whether you always tell the truth, what would you say?”
In the second case a reply of “yes” means you are talking to the truth teller and a reply of “no” means you are talking to the liar.