That's a tough one.... If someone were to ask me a totally illegal question, such as whether I planned to have children, I might be tempted to pretend I misheard it and say, "Did you just ask me if I would have your children? ??" That might put the interviewer on the defensive.
I suppose you could ask, "Did you just ask me ___? I'm surprised you would ask that." Then keep silent. I would expect that the interviewer will get the idea that the question was inappropriate and will move on.
Some questions (that I don't ask) such as "what is the last fiction book you read for pleasure?" are just a way of making conversation, assessing your vocabulary and spoken language skills and judging your critical thinking skills. If you aren't a reader, you could say, "I'm not much for novels but I enjoy [film, number puzzles, clog dancing]and spend my free tme that way." That at least gives the interviewer a topic to question you about without discussing the most recent book you've read, "Horton Hears a Who".
As for the Q: where will you be in 10 years? A: An attending.... there are so many different options as a practicing physician. Will you be in an ambulatory care setting? an ICU or other high tech environment? Are you most interested in the care of the elderly, the very young, women, the mentally ill or some other subset of the population? This is an opportunity to describe what you know about the practice of medicine and what sort of medical practice attracts you. Just saying "attending" is like somone in high school saying they want to go to college and in 5 years they hope to be a teacher without any idea of whether they'd like to teach HS or preschool and if they see themselves in a rural, suburban or urban district and a public, private or charter school if given all those choices. Where do you see yourself in 10 years is basically a "what is your entry level dream job" question. If you act like that's a stupid question, the interviewer may suspect you don't know much about the practice of medicine.