Manifistations of power means the ways that the power shows itself through you. So if I'm your boss, the manifistation of my power is through how I chose to show power over you. It can manifest itself in the way I speak with you, the way I give you work, or even by paying you money. The ways that I assert my power is the ways that my power manifests itself.
This is a tough question, and you really shouldn't expect to see it as one of your AWA questions. You have about a 1/250 (.25%) chance of seeing it. And now you will be able to answer it

Here is another way to write the prompt in easier to understand terms:
"Of all the ways that power is used or shown, restraint in the use of that power impresses people the most".
Hope this answers your question!