...just the title, not the book!
If you want to know, go to JK Rowling's official website and follow these steps:
"Click on the eraser and you will be taken to a room — you'll see a window, a door and a mirror.
"In the mirror, you'll see a hallway. Click on the farthest doorknob and look for the Christmas tree. They click on the center of the door next to the mirror and a wreath appears. Then click on the top of the mirror and you'll see a garland.
"Look for a cobweb next to the door. Click on it, and it will disappear. Now, look at the chimes in the window. Click on the second chime to the right, and hold it down. The chime will turn into the key, which opens the door. Click on the wrapped gift behind the door, then click on it again and figure out the title yourself by playing a game of hangman."
Alternatively, if you click on the subject link, the title is provided at the very end of the article.