In the Slums, found inside of the Jaffar Wheelstation Garage, on a work desk, next to a blue locker near where Zaid is working at
Gallery
Location of Jaffar's Safe Zone
The blueprint's placement on the desk next to the locker
The garage containing the blueprint. Zaid can function as a landmark for the right section of the garage
Trivia
It is an inferior version of Grill'em and Kill'em with the only benefit of this upgrade being how easy it is to receive and that it can be used on Hatchets