Dragon's Dogma Walkthrough Part 40: Reward and Responsibility

Talk to Aldous after killing the cockatrice and completing "Honor and Treachery".  He tells you that the duke has taken notice of your feats, and selected you to lead an expedition. He tells you that the journey will take you far, and that if you have tasks to complete or personal matters to attend to, to do so now, and that you will not see Gran Soren for some time.

Click on "Accept". This begins the quest:

Reward and Responsibility
Make for the Duke's Solar

Objective
In recognition of your deeds, Duke Edmun has asked you to head up an expedition. Visit his Grace afore you depart.

Details
Speak with Duke Edmun in his solar, on the castle's second level.

The Duke tells you he has some gifts for you. Follow him to the treasury, and accept the Duke's gifts. Take all you see here. The main item is a Paladin's Mantle. But there is also additional chests and bags of gold, including coin pouches and large coin pouches.

NOTE: If during the quest "The Wyrmking's Ring" you gave the Duke a fake ring, he will not be able to open the main chest where the Paladins Mantle is.  But he does not suspect that the ring is a forgery, he thinks that time has dulled the ring's magic. He tells you that he will have the contents of the chest delivered to you later, but don't count on it.

You can still get the item though. Rest until nightfall, than sneak back into the castle. Careful not to be spotted by one of the patrolling guards. Stealthily make your way to the treasury. Use the REAL ring on the chest to unlock it and get the mantle.

This completes the quest, "Reward and Responsibility". The next quest starts immediately.