I completed the quest (got message saying so) read the book, saw the 3 black circles, but got no reward. I have a save before reading the book.

Did I do something wrong at the end to not get a reward? Tried clicking on the circles, but no words of explanation when I clicked. ???

Did you click on any of the 3 choices (green spheres)?
Each offers something.
One can leave the area easily having never made any selection by rereading the book carried in inventory.

Reading the Winds of Change will take you back there even if the quest is complete, if you wish to make a selection from the green spheres.