Dorian will definitely be listing his research heavily towards Corypheus -- perusing books available in the library, going to great lengths to obtain new codices beyond Skyhold, writing to any trusted scholars back in Tevinter for more information, and so on. An indication of how far he could get would be great, and any other notes you can think of!

I can also narrow this down if necessary, just Dorian's net being cast is rather broad, if biased towards his knowledge of Tevinter history.