During GW1?
Nothing. Except to exemplimary individuals like Glint and the Forgotten, Seers, Mursaat. But they didn’t share any information about this.
The commoner in GW1 knew nothing about the Elder Dragons’ existence. And even when people saw the hibernating beasts, so much time had passed that they were covered with rock and dirt and even vegetation that they did not even come to suspect their true nature. The asura thought Primordus to be a mere statue that leaked magic. The charr thought Kralkatorrik to be an odd mountain that had scales (which we see is common place in the Realm of Torment so given that such can exist in the GWverse, it’s not such a stupid thought as we may think).
Even we players didn’t know what that giant scaley island-mountain, the beast frozen beneath the ice lake, or the giant ‘statue’ in the chamber of the Great Destroyer were during GW1 – we found out with The Movement of the World’s release shortly after Eye of the North’s release.
Common knowledge of the Elder Dragons only truly surfaced with Jormag’s rise and the norn being forced south – and even then, as we are told in the novel Sea of Sorrows, people often thought Jormag to be the one and only Elder Dragon – knowledge of Primordus didn’t become common until after Zhaitan’s rise, due to its isolation. Basically, Zhaitan’s rise was the catalyst for the knowledge of many Elder Dragons (and even that took a few decades) for the common man.
The Order of Whispers supposedly knew before then, but again, in GW1 just about no one but the survivors of the previous dragonrise knew of the Elder Dragons’ existence. And for some reason, they didn’t feel like telling.
Edit: For clarification, I am taking Vekk’s Thesis and The Six: Being or Playing God to be simple continuity oversights and thus not canon (either by those writers, or the mention of draconic energy consumption – particularly for the latter; Vekk could have arguably found out and wrote this post-EotN) as I see these, and a few other books, simply being added as Anet’s attempt to satiate the fan’s outcry for more GW1 connections (and the community fell right into Anet’s lap with that simple trick) – heck, they may even be fixed when the mention of Riannoc still being alive post-Secondborn death is/was fixed.
