Nicholas Koziolek works primarily in the theory of thought, i.e., roughly speaking, in that part of the metaphysics of mind that treats of propositionally contentful mental states and acts.
Currently, Nic Koziolek is working out a theory of belief that’s both knowledge-first and act-first, in the sense that it explains belief in terms of what he calls epistemic acts: acts like perceiving and inferring: acts in which, when all goes well, you come to know something you didn’t already know.