What philosophical approach is primarily concerned with "what do you know?" and "how do you know it?"

The chosen answer, epistemology, is the branch of philosophy that deals with the nature, scope, and limits of knowledge. It focuses on questions such as "What do you know?" and "How do you know it?" which are central concerns in understanding how knowledge is acquired, justified, and validated. Epistemology examines the various sources of knowledge, including perception, reason, memory, and testimony, and assesses the reliability and validity of these sources.

In contrast, ontology is concerned with the nature of being and existence, exploring what entities exist and how they can be categorized. Constructivism, on the other hand, is a theoretical perspective in education and psychology that emphasizes the role of learners in constructing their own understanding and knowledge based on their experiences. Lastly, realism is a philosophical stance that asserts the existence of a world independent of our perceptions and beliefs but does not specifically address the questions related to knowledge acquisition and justification like epistemology does.

Therefore, epistemology is the most accurate answer because it directly addresses concerns about knowledge and its foundations.