Do i need nike+ sensor with iPod nano 6.generation?

No. One is built into the unit itself. Some had said that it isn't quite as accurate as an external one, but results vary.

B-rock

The sensor that is built into the nano, is that just the pedometer that counts steps and calories or something else? I want to see my distance but I don't know if that is what's already included or part the the Nike+ I have to purchase.

According to this page: http://www.apple.com/ipodnano/features.html

Track your walk. Or your run.

The built-in accelerometer in iPod nano gives you real-time feedback on your workout, and you can upload data to the Nike+ website. There’s no need to connect a receiver or use a shoe sensor to track your steps, distance, pace, and time. Just clip on iPod nano and go. In the gym, connect iPod nano to a Nike + iPod compatible cardio machine to keep track of every workout. Back at your computer, upload all your data to the Nike+ website to create personal goals, check your progress, and challenge your friends to top your results.Learn more about Nike + iPod

B-rock

You need the kit.

The clip above details "Nike + iPod compatible cardio machine." It's unlikely you're using one.

I learnt the hard way. Purchased the nano thinking everything was built in, and then had to purchase the Nike+ kit.

You don't need the sensor though.

B-rock