Class quests are always given at the Guild for your class by it's Guildmaster (for CNJ this is E-Sumi Yan in Stillglade Fane in Old Gridania). Class quests end at level 30, after which quests for it's Job upgrade replaces them. Either way, go back to the CNJ's Guild and speak to E-Sumi Yan and he should have a new quest for you.