If I have two addresses at one site, like this: www.site.com/one www.site.com/two Do both of them contribute to www.site.com's Pagerank?
I'm not hundred percent sure on this but no. From what I know PR is counted for the number of backlinks a certain URL has... not for the number of backlinks a domain as a whole has. But like I said before, I'm not hundred percent sure.
Pagerank is a web page value, not a website value. All your web pages will have their own unique Pagerank value, it just happens majority of the time internal web pages have the same value site wide, with some being higher due to popularity of that web page. Every actual URL that renders HTML will get it's own Pagerank value, this is where Pagerank dilution and duplicate issues also come into play, but thats for another thread.
Furthermore, those are not subdomains, they are directories. Subdomains look like this: sub.site.com (with the subdomain being "sub" in this example). Not only that, but they are also no longer treated as separate sites or "domains" by Google anymore.
Each and every single page of a web page has it's own pagerank, so if You for example write great tutorial and people link to the site, it's possible that the page has even higher pagerank than the main index page