Look on the frame nest to the handle bars
How To Find The Year Model Of My Yamaha Motorcycle?
Or you can take your VIN to the local Yamaha shop and they can give you a wealth of info. On your bike,
Do you have any of the motorcycle information still left on the bike? If so you can take that or contact your local DMV( Department of motor vehicles ) and they can look up the bikes information and history for you so check for the vin number on the bike.