As commented above, the only bookshelves that generate book 1 of the skill books are on the base game library lot in Willow Creek. The bookshelf you need is not in build mode, even if you use the bb.showhiddenobjects cheat. I, like others, have saved a room to the gallery with the bookshelves in it. You can add it as a basement room with no access, it still turns all bookcases on the lot into ‘library’ bookshelves. Here’s a link to one of a few threads on the forums about it. https://forums.thesims.com/en_us/discussion/797586/help-no-skill-books-in-library
I have tried the spawn cheat but it’s a little dangerous as you need to make sure your sim is on the lot or the bookshelf will spawn in the surrounding neighbourhood. I also have an edited version of the Windenburg library on the gallery that already incorporates the required bookshelves and also makes it toddler/kid friendly.
It would be nice if the required bookshelves were added to build mode, even if if they were hidden and required the bb.showhiddenobjects cheat. 🙂
Thank and regards,
Jennifer