The Imperial Archives are in the Silver District of Dragon's Throne.
There are different stacks, with a number of books that can be investigated, but only reading (or at least skimming through) a book will tell the reader if it's one that's needed as far as the proper forms and information goes. Once the relevant forms and information is researched, it can be notarized by the Imperial Notary, an elderly gentleman in the middle of the archive - and someone who Master Deng thinks may be the most dangerous person in the building, at least in some strange non-fighty fashion.
It includes the book "Speculations into the Fate of the Emperors", which contains half of the mechanic for proving someone's Imperial lineage. Completing that takes hundreds of successes.
To be allowed to do research, you have to make three 10 success research rolls in ten minutes with only the research skill, no other skills that might normally apply. (That's a new mechanic.)