Theory of knowledge.
A considerable part of philosophy consists of theories of knowledge, but much of it is arid or prejudice, especially if indulged in without benefit of knowledge of real science.
There are two basic fallacies in much epistemology:
(1) The Kantian one, that one can say what knowledge is, without saying - first - what there is that one has knowledge of, and
(2) The postmodern pretense that small careerist dishonest minds have or should have the powers to dogmatize on what is and is not "knowledge", by what is essentially a public game pf pretense and public relations.
In general, if you want to have knowledge or know what knowledge is or may be: Study real sciences and mathematics, rather than academic philosophy or lit.crit.
See also: Ontology
Ayer, Carnap, Edwards, Nagel, Nagel & Cohen, Scheffler,