Dual Class Certificate Manager:
The Dual Class Certificate is given out when a character's main and dual class reach Lv. 85, Lv. 90, Lv. 95, Lv. 99, Lv. 101, Lv. 103 and Lv. 105.
Later you can receive an Enhanced Dual Class Certificate. It is given out when a character's main and dual classes reach Lv. 107, Lv. 109 and Lv. 110.
Upon receiving both the regular and the ehanced certificates you can learn new skills.
Keep in mind that skills you receive due to a certificate are available to you both in you main and dual classes.