In Japanese, the word deshyoo shows that the person speaking is either being politely vague or isn't sure about something. Deshyoo ka is asking a question with that same uncertainty. Saying deshyoo ka ne is asking a question and looking for confirmation more from yourself than the person you are addressing.
My tutor Dave says, "It's more of an personal question than a real question. Like 'Oh yes, where is it, anyway?' You're asking yourself, not the other person."
"So basically," I say "It's an internal question said out loud." He tells me that's correct.