@MelosaofRados Hello! I did a little research and found this old thread on the forums.
https://forums.thesims.com/en_US/discussion/910804/anyone-getting-this-vampire-aspiration-bug/p2
Some folks there were saying that you may need to have your sim read the book again, possibly even 2 or 3 times. When you click on the book, do you get the option to "reread"? If not, then you may want to have the sim continue reading for a few hours. It's possible there's a hidden counter that will keep ticking and eventually complete the aspiration goal. Another simmer said theirs completed after an exit and reload of the game. Maybe have your sim reread the tome for a few hours and if nothing changes, then save/exit the game and reload. Then, if you're really desperate, you could always cheat the aspiration as @xochiquetzl_xkvn suggested. Good luck!
