All of the class upgrade quests work basically the same way. You level you class up to 30 and complete all the class quessts, you get the MSQ storyline to the low 20s(quest needed is i believe Sylph Management), then an NPC in your classes guild hall will offer you a new quest to upgrade to the related job(lancer -> dragoon for instance). Then when its time for the next job quest, go to where your NPC took you previously and they should be waiting. It sounds like the dragoon quests(after the first one) start in CCH.