1. Who knows? It all depends on how they intend to implement this DNS blocking. I'd expect non-US ISPs would stop using any US-based root nameserver, circumventing the block. Considering most of entities taking care of the root zone are either American institutions or US-base multinationals, this would really pout a strain on the existing non-US infrastructure, but could actually result in a better designed network (i.e. less reliant on US bodies).

2. Yes, blocking access to foreign websites is the whole point of the legislation. Note that this would only mean that US-based users wouldn't be able to resolve your .dk, but everybody else (i.e. in Europe or Asia etc) would still be able to do it.

3. Good question. Again, this will depend on the technical implementation; I believe at the moment they're only talking about blocking DNS resolution. The minute they block IP-based connections, you basically have the Great Firewall of America in place.

1. That's complicated. It only directly affects US citizens. But indirectly, foreign companies, websites etc could be affected.

2. Are you talking about the entire TLD? Then, no. If you are talking individual domains, then, yes, those are the targets of this bill.

3. ThePirateBay is exempt from SOPA DNS-blocking since it is a dot-org. IP-addresses are exempt of course from DNS-blocking. Plus, it looks like DNS-blocking has been pulled entirely from SOPA (but let's watch that play out). AFAIK no one is exempt from interfering with payments from advertising and payment processing companies.