How Can I Be sure I Know Something?

This question is a rather difficult one to answer, mainly because there is no real right or wrong answer to it. It could take a lifetime of thinking to properly answer it, but I don't have that long so ill do the best I can!
The first answer that immediately popped into my head when I first read the question was that "we cannot be sure we know something, we can't be sure we know anything, we can't be sure we know everything". I say this because if I was sure that I knew everything then I wouldn't have to question what I know, like I'm doing now. …