Your trainer wants you to use your new skills to prove that you are ready to face the many dangers that exist in the world.
'I welcome you to Archet, fellow Captain! I specialize in teaching warriors such as yourself useful skills and abilities. I presume you are here for just such a purpose, so here is a word of advice:
'Remember, a Captain does not best serve his companions by running recklessly into the fray. Nay, it is when he stands behind and directs the efforts of his fellows that he truly shines. There he can see weaknesses in his enemies or press his companions forwards and inspire them to victory.
'Show me your skill by using Devastating Blow.'
HINT:
Captains rely on their Battle Shout to put them into a Battle-Readied State. While in this state, Captains can use special skills such as Devastating Blow, an effective attack that deals a great deal of damage. Attack the Training Dummy with your Battle Shout to put you into a Battle-Readied State and then attack the dummy with your Devastating Blow.
Use Devastating Blowon the training-dummy nearby.
HINT:
Captains rely on their Battle Shout to put them into a Battle-Readied State. While in this state, Captains can use special skills such as Devastating Blow, an effective attack that deals a great deal of damage. Attack the Training Dummy with your Battle Shout to put you into a Battle-Readied State and then attack the dummy with your Devastating Blow.
The Captain Trainer is in the training grounds of Archet, very near the gate.
Now that you have successfully used your newly-learned skill, you should return to your trainer and tell him of your success.