Quick Answer
Community guides commonly describe the flow this way: complete the Ancient Magic Record excerpt task, receive the Evolution Slate, then study it to master Evolution Power. The screenshots here correspond to Magic Handbook Volume I and the Windrest Province Chapter 5 required lesson.
Where to Accept the Task
Use the left-side quest panel instead of searching the bag directly. Open the task menu, stay in In Progress, then check the Lost Items category for the Magic Handbook or Ancient Magic Record related objective.
If the task has already been completed, it may no longer appear in the active list.
Where to Complete It
After accepting the task, follow the quest tracker to the indoor counter area and interact with the book marker. In the screenshot, the tracker points to opening the Magic Handbook.
Steps
Open the quest panel, choose In Progress, find Magic Handbook Volume I under Lost Items, confirm the Chapter 5 required lesson objective, then go to the counter shown in the screenshot and interact with the book marker. Completing the study step gives the Evolution Slate and leads to mastering Evolution Power.
Evolution Slate vs Evolution Power
The clearer wording is: the Evolution Slate is the key reward or study item, while Evolution Power is the ability learned from it. Players searching for Evolution Power are usually looking for how to get the Evolution Slate.
If You Cannot Find It
Check three things first: whether the Chapter 5 prerequisite is unlocked, whether the task has already been completed, and whether you are looking at the correct quest category. Completed tasks may disappear from the active list.