There is only one suggestion that I can make. Ignore the Alien quest and work on advancing another quest. Then once you completed what you can do in another quest, come back and revisit the book. I had a similar experience in multiple quests in this game. One story would seemingly freeze, unable to advance, then I advanced another quest, returned and the stuck quest is then unstuck. I had this happen multiple times. I've played this title since it first posted so try that... advance a different story, then return to the alien thing. If it still hasn't triggered then you may need to advance another story before the alien book triggers. This same thing happened to me with the vampire book not disappearing but unable to be read until other events transpired, the principal not showing up in her office for the alien quest until I advanced the boxing quest, XVideos not triggering initially until I advanced something else and I'm fairly certain my alien book disappeared for a time as well... IDK for certain as that has been a LONG time ago...


Yeah... it's a real thing... Do something else and come back later on...
I hope this helps you. Adventure ever on, Phat

PS: I've been trying to think how this went again and I think Lily, the book store clerk, actually GIVES you the book rather than you having to buy it. That may be why it disappears as I do remember buying every book as soon as it became available for sale. I'm pretty sure the alien book disappeared on me too so run another quest and come back and talk to Lily again... in fact you could try talking to Lily now rather than engaging her sale inventory...