To sceptical outsiders, the philosophical investigation of knowledge (epistemology, that is) might seem like an argument over nothing. Can't we simply answer the biggest question - "what is Knowledge" - with a link to an online dictionary or, failing that, a brief explanation of semantics and the nature of context? In other words, 'knowledge' means nothing on its own; its meaning is derived from the sentence in which it sits. You can draw out general senses from this and list them in a dictionary: "being aware of a fact", "familiarity with a concept", "practical skill in a certain area". Capital-k Knowledge has no existence unless it's defined, and the definition is essentially arbitrary; that is to say, almost every possible definition is equally valid.
This is wrong! To see why it's wrong, consider a field of discussion with obvious value, like car mechanics. It's obvious that there's meat there, that there's something of interest to be studied. However, try defining 'car' or 'engine' properly. The same problems that come up when you define 'knowledge' are here as well. Isn't 'car' used in different ways by different people? What counts as an engine? Can you construct an elegant definition that rules out trucks and buses without ruling out actual cars? Ought broken cars and engines count, and if so, where do you draw the line? And so on. Nevertheless, it's still possible to learn how to fix an engine without once touching the tricky philosophical problem of definition.
We drive our knowledge around every day: trivially, whenever we tell other people things. If you make a surprising claim about reality, you're likely to be asked 'how do you know that?' Whether you're a philosopher or not, you need to be able to answer that question - and, in order to do that, you need to have some vague idea of what it means to know anything in the first place.