What is the gross weight of a kenworth dump truck?

Varies by state/national law. Typical allowance for a tandem truck would be 54,000 lbs gross weight, regardless of manufacturer.

When you get into a state such as North Carolina, which has some very idiOSyncratic bridge law weight, and which may vary by the vehicle's wheelbase (and, I might add, only applies to intrastate vehicles, while interstate vehicles aren't affected by this), it gets a lot more complicated.