This is a slight case of “most of the story is in the headline” I’m afraid, as there’s not a huge amount of additional information besides the fact that, yes, Blizzard says World of Warcraft is getting a Gamescom expansion reveal.
It’ll be happening live in Cologne, Germany on 6 August at 9am Pacific Time (so, uh, about 5pm in Germany, I think?) But if you don’t happen to be there, it’ll also be live-streamed.
More details about how to watch that will apparently be coming from Blizzard’s dedicated Gamescom page. I’d imagine said page is the one they’ll be using to stream their World of Warcraft stuff.