Sometimes, we use question words like "what" in statements instead of in questions. For example, compare "What are you saying" (a question) and "I don't know what you are saying" (a statement). In Japanese, the question-marking particle か (ka), which usually marks a question, can be used in both ways. To ask "What are you saying," you may say, "何を言っているのか" (nani o itte iru no ka), using particle か (ka) to mark the question. To state "I don't know what you are saying," you may say, "何を言っているのか分かりません" (nani o itte iru no ka wakarimasen), an extension of the former. Here, か (ka) helps us in an interesting way. An English speaker, for example, may interpret this statement as, literally: "What are you saying? I don't know." It's almost as if the speaker asks themselves a rhetorical question only to respond with their own statement.
Source: tatoeba (12767696)