@Fil Albuquerque,
A different situation entirely is not knowing about X in any way, not even that there is X in which case you cannot question X.
When we talk about imaginary objects not existing, we are not being entirely objective as imaginary objects exist as concepts and concepts are REAL concepts, that is to say, imaginary objects are in the least real imaginary objects, thus a part of reality...questioning reality immediately confront us with this problem, because we refer to it in the question, we have assumed it. Thus we don't need to know anything more other then there is a X so that there is a reality is proven.