Dragoon upgrades from one of the starter classes, Lancer, at level 30. If you didn't start as Lancer, you can unlock the class at the Lancer's Guild in Old Gridania (x14.0, y6.0), starting at level 10 by speaking with Jillian. Once you have reached level 30 as a Lancer and finished all seven class quests, you can return to Jillian to get the quest Eye of the Dragon. Upon completion of this quest, you will obtain the Dragoon job stone, unlocking Jump in the process. Equip the stone from the last tab in your Armoury Chest to become a Dragoon.