The Dextrous is a title quest given by the Councilor of any race's capital city. This quest is the last of the three title quests available to increase your dexterity. It consists of killing 50 Raptors. These monsters can be found all over Agon and even on the 4 smaller continents. You may only get it/turn in the quest at your race's capital city (ou must have done the first and second part before you can do this one).
The reward is a permanent +6 bonus to dexterity. As the final quest, the total bonus you will receive for all the three quests will be a +12 bonus to your dexterity.