ByoingG 25

Click in the Left Stick while choosing a category or answering a question, and the bobblehead on your desk should start shaking.

I'm not certain if you need to do this more than once but I got "Head Bobbler" after doing it less than 10 times during a question when I did it the first time.

At the end of the game, this should unlock. You (or one of you avatars if you are playing Study Mode in more than singleplayer) should get the title head bobbler to show up eventually in the final screen.