How do tales of adventure work?

[Zugabe]

A couple things. Do you have to own the job or does it unlock it for you?
Like if you have the expansions required for the job but you don't have the job itself unlocked in the game?

[Rongway]

You can buy a job boost for any job covered by your registered expansion licenses. If you have not unlocked the job already, using the item will unlock the job for that character. For more information on job boosts see the Job Level-Boost and Scenario Skip Item Guide.