To unlock the Master Talent trophy in Anthem, you will need to increase the Gear Score of one of your Javelin's until it reaches the Masterwork (yellow) level. The Gear Score required is 640. The overall Javelin's level must be Masterwork.
The gear score is an average of all of your gear. The higher the score, the higher the rarity. Once you have reached the Masterwork level with a Javelin, complete a mission, contract, or stronghold and the trophy will unlock at the end.
UPDATE: The patch on March 9th, 2019 raised the power level required to 640.