You will gain points to unlock perks for your character whenever a 'specialist' companion kills an enemy.
This is the best weapon in the game, it is silent, accurate and capable of taking out Peggies with one hit. You will find one in the Silver Lake Boathouse which is located on the west-side coast of Dutch's island. To reach it you must swim inside, climb up, and interact with the power switch on the wall. Grab the Boathouse Key from beside the door, use it to open the door, then head back to the shed. Turn the wheel to the left of the shed to pump out the water, then you can open the hatch to gain access to the prepper stash. Once inside there will be a wooden barricade you must smash to access the back room, and it’s in the back room along with a decent amount of cash.