I've been given the second word of Bend Will by Hermaus Mora, but when I look at the black book to gain one of the powers nothing happens. How do I activate the book? There doesn't seem to be any option to do so.

Did you click the Book? Or one of the three glowing spheres floating above the book? You have to click the sphere to get a power/ability.

I'm not trying to belittle you or be sarcastic, I ask because I made this mistake before I figured out the difference after two trip back and forth between Solstheim...