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Thanks for the answers. For some thing Google treats a subdomain like a subfolder but for other things like a different domain, that's why I don't see it clear. Any experience doing it when the subdomain is a blog?

You could use Xenu or Screaming Frog to pull out all their page meta titles (assuming they are optimized for keywords). To find the keywords they are really going for, use something like MajesticSEOs frash crawl index to see the top pages they are building links to... the anchor text used will be the give away.