Of course the Matrix itself is an adaptation of Plato's cave with a hearty scoop of Descartes' evil genius (and many other things, I'm sure) in the mix. Humanity is chained to the wall by the machines, who are putting on the shadow puppet parade. Of course, if all you saw was metaphor for things, but not actually the things, then it could be said that you have no true knowledge. But in this case, the machines have duplicated the actual world almost perfectly. Since this is the case, if I said to someone who had never seen corn, "Corn is like this piece of pseudo-corn" and handed him a mass of lab grown cells that have been genetically engineered to perfectly simulate corn in shape, texture, color, flavor, and all other respects, then can they be said to have no true knowledge of corn? If not, then what constitutes "true knowledge"? Neo's knowledge of language still counts as being perfectly true in the world outside of the Matrix. Is it not true to say that his knowledge of the objects attached to the words that he learned in the Matrix are also truly known?
The real problem is that we are limited by our brains' ability to perceive the world. We are, after all, not omnipotent or omniscient, so there are many things from the outset which we must take on faith. For example, there was a time when I didn't understand a thing about the properties of mass, but I still trusted them to keep me from falling through the planet or flying off into space. What can we ever truly know? We are absolutely impaired by our size, shape, lifespan, and every possible situational condition to which we are subjected. All of it defines our ability to "know" things. I don't think there is anything that "we" can be sure of. The only thing that "I" can be sure of is that I exist in some capacity; I am experiencing a universe in one way or another, and hold a mental impression of my self and what that means to me from moment to moment. I cannot be sure that any of the experiences that I recall from the past have actually happened to me or not, but I can be sure that however those experiences got there, they are what constitute my identity, and determine my actions in any following event.
This is a difficult statement to make, and tricky to defend without accepting some preconditional arguments, but I'm willing to overlook this on my blog which nobody reads. ALSO POOPY, HAW HAW HAW.