Bookcase Skillups
 

is there anyway to make a mod to maybe show o the reticle whether a bookcase will offer a skill up or which bookcases you've already examined?

Books are not fixed to shelves, they're selected randomly when you pick them. You can read everything in a Mages Guild hall, come back the next day and find a book you haven't read yet.

Yes, they works as containers, in fact when you interact with a library, you loot the book and it's automatically read. Same as barrels, etc.

Each book guive you some rewards, exploration or standard xp, or also special xp (craft..) with a cap.