This question already has an answer here:
Universal Skepticism seems to boldly claim certainty in the knowledge that knowledge is impossible. The obvious contradiction here is that if they really believe their own theory, it should force them to conclude that there is no way to know that the theory is true, because the very nature of their theory says that knowledge is impossible. This should then open the door to other arguments, since now a universal skeptic is forced to conclude that they have no way of knowing if knowledge is impossible, so they have no reason to put their somewhat arbitrary skeptical beliefs above any others. They should believe what has the the best justification, even if certainty can't be guaranteed, as opposed to only believing that they know nothing.
Would't this really just mean that they are no longer universal skeptics?