Well, if by “world” you mean the true nature of the whole of reality, that does not exist as something we could possibly know. But everything else except the world does exist. In his review of Markus Gabriel’s Why the World Does Not Exist, Richard Wolin explains all this and more.
Steven Poole’s review of Jennifer Nagel’s Knowledge: A Very Short Introduction is a nice overview of what we can know about what we can know. “Does any of this really matter to non-philosophers? Yes, and for two kinds of reason. The first kind is sociopolitical. Arguments about what kind of testimony (eg from scientific experts) we can trust, and therefore gain knowledge from, are evidently germane to major public issues such as global warming. … The second kind of reason for why thinking about knowledge might be important is more personal. It boils down to this: how worried are you about whether you are a brain in a vat? Versions of this idea have been put about through history by that imp of the perverse known as the sceptic. The sceptic insists that knowledge of anything at all is impossible.”
Philosophy is a bunch of empty ideas. Or so Peter Unger, a philosopher who has written quite a few impressive works of philosophy, now claims.