"Are you talking to yourself?"
Translation:Kendinizle mi konuşuyorsunuz?
If we were to include the pronouns here it would be: Sen (subject) + senin (possessor of the "self") + kendinle (the possessed self that "sen" is speaking with) mi konuşuyorsun? Naturally, we leave them out because "Sen senin kendinle" is a silly mouthful, and all the info we need is in "kendinle".
In your sentence, the "self" doesn't have the instrumental (-le), and "sana" is in dative, so (to me) it looks like: "To you your self are you talking?"