One idea I've been thinking about is to make Libraries take a "book collection" to build, and make small workbenches consisting of a table and chair. Writerdwarfs could work at the small workbenches, producing essays. Once a sufficient number of essays have been produced, an organizer could edit them together into a chronicle. A sufficient number of chronicles could be combined to create a collection of chronicles or a dwarven history or something. Similar trees could exist for accounting (census?) books, genealogies, etc. Once the collection was complete and the library built, Librarians (organizers? Teachers?) could use it to compile "study-guides or reference collections," consumable resources that other dwarves could use to gain experience in a variety of skills. A variety of book-themed creatures could drop intermediates to speed this up, including a megabeast with a whole collection.
Another possibility is individual books on various subjects that your dwarves could pass around and gain skill from. These would have to be artifact level rare, however. One could imagine combat manuals that could be created by weapon smiths in strange moods, and armor training manuals created by armor-smiths. Demonic books capable of training multiple skills could exist.
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How good is the trade system right now, anyway? If you have a fortress that churns out a lot of books etc and gives them to traders, will those books be brought as trade goods to your next fortress?