This trophy is titled "Ikora's Protégé
" and requires the user to unlock each of the Warlock's subclasses.
The initial subclass you will start with is the Dawnblade
At level 7, you will receive a Broken Relic from any type of chest you find, or earned, scattered around zones. This will give you a requirement of killing enemies, in any game mode, that will lead to a mission to unlocking the Voidwalker
At level 15, another Broken Relic will be obtained from a chest. Again, kill enemies to receive the mission for the Stormcaller
That will unlock the trophy for you only if you play through the original campaign. If you're reading this after Forsaken has launched, like I have, you will receive a boost on the character selection screen for any character that hasn't reached Level 30. Using this will boost you to Level 30, unlock all three subclasses, but not award the trophy.
To unlock the trophy after using the boost, you must progress through the start of the Forsaken story missions. You will have to return to the Traveler and speak with Ikora. She will give you a mission in the new zone, the Tangled Shore. While there, orange and yellow health enemies will drop feathers. Pick them up and complete the story mission to unlock the Tangled Shore fast travel. Return to the Tangled Shore and concentrate on doing Public Events. This will reward you with the most amount of the feathers. After about four events, that should update the mission from Ikora, which tells you to travel to Io.
Select Io and a large orange triangle will be on the map in the Lost Oasis. Select this mission, Visions of Light:
During the mission you will receive a Seed if Light. Use the Seed of Light and complete the mission to unlock Ikora's Protégé on your boosted character.