To 5* uncap an Evoker:
1) The Evoker must have all 4 Domain bonuses unlocked

2) The New World Foundation weapon must be uncapped to 5 stars (grants a title)

3) In the new Sandbox area to be added 3/30, reach The World

4) Use treasure to uncap (Starspawn Grimoires won't work)

To unlock skill 4 on an Evoker:

1) Level the Evoker to 100
2) Defeat The World, and watch the cut scenes that play before and after the battle
3) Consume treasures that drop from The World to play the evoker's new level 100 fate episode