Well whatever kind of questionnaire you prepare keep in mind that Nano is not tested as yet so there should not be any questions on mileage, performance etc. as these cannot be judged now, so adding some questions
1) How are the looks?
2) Are you satisfied with the colours available?
3) Is it comfortable to sit, can three people be accommodated comfortably behind?
4) What kind of journey you think Nano is suitable for? Here you can divide your questionnaire on demographics basis. so you can ask young college going folks if its suitable to take to college? Then you can ask house wives if it is good to travel short distances and so on...