Final answer:
The not represented key concept of existential therapy in the student's question is the absence of a transcendent foundation for societal structures, contrasting with the central existentialist beliefs in human freedom, existence preceding essence, and personal responsibility.
Step-by-step explanation:
The key concept of existential therapy that is not represented in the student's question is the existence of a transcendent foundation for societal structures. As outlined by existential philosophers such as Sartre and Camus, existential therapy revolves around the core belief that existence precedes essence, meaning that individuals first exist and then define themselves and their essence through their experiences and actions. Additionally, existentialism emphasizes the importance of human freedom and the responsibility that comes with it, as well as the authentic recognition of one's emotions and the lived experience of others. However, existential theorists would assert that societal structures and ideas are not pre-existent or necessary, thus challenging the idea of a transcendent foundation that qualifies them for objectivity, a concept not reflected in the student's question.