You must complete a series of trials for him. The trials are initiated by clicking on the door at the bottom of the elevator in the Vallon Foundry ( 312, -114, -111 ) . After completing each you should return to Grozmag the Trainer.
The first trial is easily soloable, it consists of killing a single a Zek Berserker.
NOTE: When you speak to Grozmag after this trial, be sure to tell him that the battle was exhilarating, otherwise you will have to restart the quest!
The second trial consists of 4 level 32 a zek berserkers, a dark knights and defilers. Two of them are ^^, and the other two are solos.
The third trial is another solo step. It is two orcs, a pummeler with a down arrow and a warrior with no modifier. Both are level 33 solo mobs.
The fourth trial consists of one ^ mob and 4 normal level 35 group mobs. You will need a group unless you're 44+.
The fifth trial is another solo step. It consists of a level 36 Zek Defiler, a single down level 36 Zek Berserker and a level 36 double down Zek War Wolf.
The sixth trial is a group step that consists of a level 38 ^^^ champion, a 38 ^^ single inquisitor and 2 level 38 weald wolves in a group.
After completing all six trials you must kill Emperor Fyst in the Deathfist Citadel. Return to Grozmag after doing so to complete the quest and receive your Shiny Brass Shield.