To unlock this trophy you have to complete "The Final Test" in the Prologue
Once you have completed the mission before, which is "Freeform Training", choose "The Final Test" and you will load into the mission. In The Final Test, your target should be someone named Jasper Knight. In this mission, you can tackle it however you want but I recommend you follow the mission story because it completes this mission very easily.
Once you have completed The Final Test, you'll unlock "Cleared For Field Duty".