For this trophy you need 100 kills with the Stalker ship. Here's a few tips based on how I like to play the Stalker and hopefully it helps.
First some basic information, the Stalker is a cargo ship which means average health and speed but can carry much more Ore to upgrade outposts with, typically weaker in combat. The Stalkers primary weapon is a moderate ranged machine gun that does moderate damage which can be useful.
Now the build, there'd a few ways I play this class, some revolve around using stealth and EMP to single out and enemy while others are easier to use and use your charge up attack and machine gun. Personally I don't recommend worrying too much about core on this class, you can use your remaining points on core if you want. The most simple build is to max you machine gun and charge up attack while the remainder goes on core. As for the stealth technique you'll want to focus on maxing EMP, stealth and the remainder on your machine gun for the easy 1 on 1 stealth kills.
When playing the Stalker you'll want to decide whether you want to play with the team or go it alone and take out loose enemies. If you decide the first choice it's the same as most basic offense strategies, stick with the team and fire off your shots in the enemies direction. If you choose the latter then you'll want to find a good place to camp in stealth and wait for an enemy you can EMP and kill, you should be able to kill most non-combat ships before they can escape the EMP.