This study examines how the Korean interrogative ending –nka functions across spoken and written discourse and addresses three research questions concerning its interactional purposes, mode-specific distribution, and pedagogical implications. Spoken telephone conversations and written newspaper texts were analyzed to capture distinct discourse ecologies. Using data drawn from the Linguistic Data Consortium (LDC) Corpus and the Sejong Corpus, the study conducted a qualitative discourse- and interaction-based analysis to identify the functional patterns of –nka. The findings show that –nka is used in spoken interaction to manage uncertainty, seek confirmation, and formulate self-addressed questioning, whereas in written discourse it serves rhetorical and issue-raising purposes tied to stance-taking. These results suggest that teaching –nka requires attention to genre-specific functions and epistemic stance management. The study thereby highlights the pedagogical value of integrating discourse context into instruction on sentence-final endings in Korean.