Dragoon need lvl 30 LNC, 15 marauder. I already have a lvl 20 pug that I played during phase 4.
The dragoon quest giver at lancer guild, you will need to clear all your class quest until the lvl 30 class quest.

Dragoon only can take skills from pug & mrd, and the skills are the same skills that you can take as a lancer