When your wife/girlfriend says "I don't know what I want, what do you want to eat?", She's not really curious about your preferences, she wants to see if you can guess hers. I recommend you just tell her to get in the car and let it be a surprise. She'll tell you where she wants to go really quickly.Probably the exact words in my girl's head when I ask her where she wants to eat dinner. Or ask her anything, really.
She figures out what she wants immediately after I choose. She chooses "anywhere else".