How can we locate my trasis number of my nissan pick up car?

Chassis number? Do you mean VIN? The most common place to find your VIN (Vehicle Identification Number) is on a small metal plate attached to the driver side top of the dashboard close to the windshield. In fact, it should be visible through the windshield.
Other places you look:
Vehicle Identification Label in your Owner's Manual
Stamped on the frame under the front hood
On a sticker on the driver's side door pillar
On state vehicle registration certificate
On the vehicle title of ownership


Read more: http://nissanhelp.com/diy/common/nissan_vin.php#ixzz31kTlaL7h