Suppose an officer were to ask "Do you know where you are?" I wonder under what types of responses could constitute probable cause for DUI, considering that there would be no reason a stopped motorist could consider his present whereabouts a personal secret. To be sure, some non-DUI motorists might be lost, but I would expect they'd be able to clearly tell the officer something of where they were trying to go (not necessarily their destination; perhaps a road they were looking for). While there may be some motorists who would rather remain lost than let a policeman know what they were looking for, I would think most motorists in such a situation would be glad to have assistance.
It's not a matter of being considered a secret. I don't have to answer the question because I don't want to. No other reason is necessary. Refusal to answer does not create reasonable suspicion, which is the standard the police must use.
If one were drunk, any DWI attorney would tell you shutting is the most prudent course of action (not that I have experience with that, mind you). Shut up and hand over your license, insurance and registration if applicable. Those are the only things the police are entitled to.