Efficient Killer Trophy in Terminator Resistance

Towards the end of Chapter 10: Hideout and before returning to Pasadena for the Main Quest "Back to Pasadena", you'll need to speak to Ryan. He'll have something for you: A Termination Knife. As he explains, these are knives that can instantly kill a Terminator in one blow but the downside is that this has to be done stealthily. There will be two knives on the table next to him but you can always craft more once you unlock Crafting Level 3. You need to equip it like any other weapon so swap out one of your weaker weapons for it via the Inventory screen to bring up the weapon wheel and use the to highlight it.

Your first opportunity to get this trophy is during Chapter 11: Pasadena, because the area is crawling with Terminators so find one and kill it. You'll need to silently creep up behind a Terminator and once the button comes up on your screen, press  to perform a Stealth Kill. The trophy will pop once the Terminator is toast. An easy spot to get this done, is in the area to the South East of where you do the No Hope trophy because there's a T-825 model Terminator patrolling a route between two destroyed containers/vehicles. All you have to do is wait behind the bottom container/vehicle and use your Ultra Vision Goggles to track his movements so when he reaches your location then turns round, you can sneak up behind him and stick the knife in. See below for a screenshot of this location: