How do you know what you know?

This question, I think, is one of the most frequently asked questions of philosophers. Asking this question is a never ending discussion; you can ask how you know what u know, and then how do u know that u know what you know, and so on and so forth. I don't think it is that deep. I agree with the philosopher (whose name escapes me at the moment) who said "I think therefore I am." I agree with this literally, and in a more abstract sense. I think at a simple level, if you know you are something, and other people know you as something, then there is no sense in question whether you are that thing. It's all a question of perspective. Whose perspective are you looking from when you ask the question how do you know what you know? I think it is inefficient to ask questions that that don’t really have an answer. Unless you can find a tangible problem that can happen if you don’t know the true answer to this question then trying to search for it is a waste of time. I also think that if the majority agrees on something then it is true. For example, the majority of the world believes that the earth is round. Since we think it is, and we think we have proved that it is then it is. You know what you know if enough people agree with you.