You get these through doing client orders for "class trainers", which are class specific characters you see scattered through the gate area. You need to do these as the class you want the points for. After doing certain orders for them, they will have a mission that gives +5 skill points. After completing it, you get another order for 5 more, and lastly, you will be getting orders to give them class x cubes, which are cubes you get every time you "level up" a class after level cap. You get these missions one by one until you reach 10. So in total, each class specific trainer (or most of them, not sure) should give you
Edit: Correct quantity noted by @Jamesmor , who has done the content already.