What book can I read your understand more about the Cosmere, Investiture, Adonalsium, Shards, worldhoppers, and the cogs of the universe in general?

[The Night Watcher]

Only heard whispers of this stuff. What book do I read for information?

[Yata he/him]

I believe the Mistborn's trilogy is the better source of general information about the Realmatic for now. You could grasp the basic mechanics of magic and Shards. Much more is a complete product and makes a good work to explain stuffs....But you need to extrapolate from the books

[Calderis he/him]

Well, there's hints in all of them. It's all piecemeal. 

To really get into it though, you've got to start digging in Arcanum.

We know more of realmatics from WoBs than from the books. 

[Maelstrom he/him]

If you want to find a book with a lot of hints facts, you should try Arcanum Unbounded, as it has many hints facts that were not well known before. 

However, it is a short story collection, and I've heard some people don't like those.

You still will have to check WoB's and the forums for more tidbits of cosmere-ish things.

Good luck!

[The One Who Connects he/him]

4 hours ago, The Night Watcher said:

Only heard whispers of this stuff. What book do I read for information?

Most of these things are secondary to the actual story, and become background elements in the books.

The Shards are a little more involved nowadays than they were, but most of our details are still from outside sources(Brandon/Peter/Isaac).

As we get further into the Cosmere story-line, the other elements will become more primary too(worlds becoming more advanced, worldhoppers becoming more common, Dragonsteel, etc..), but there are some things that even Brandon can't fit into the stories. Details from events before/after the books, for example.

[Farnsworth]

The coppermind is our wiki, and it has TONS off infornmation. Just look on the Cosmere page or the Adonalsium page, and it should clarify lots. I’ve been madly obsessed for over four years, and I still look there sometimes.

[Nathrangking he/him]

The emperor's soul also provides a fair bit of realmatic theory in terms of the realms which impacts later stories.

[Themasterhunter]

Elantris, Warbreaker, and Stormlight is where I found a lot of helpful hints that especially reference shards.

adonalsium is only referenced in book once I think.