Noob question, if a.com gets a certificate, then b.a.com can use the same cert, right? As in the example of the fb impostor in 000webhost. So, in that same vein, can a TLD get a certificate? For example, com gets a certificate, so now anything.com has a valid certificate. Also, can I issue a cert specifically for d.c.b.a.com?
No, you can't get .com. Typically, at least for known root CAs, you have to prove ownership of your top level domain. If you own a.com, they'll ask you to either put a file on a.com/random, or register random.a.com. If you try to do so with .com, you'll likely fail (but please feel free to try and prove me wrong!).
Yes, you can get a certificate for d.c.b.a.com, I don't see any reason why not if you own a.com. Unless your specific root CA has constrains on the depth of the domains.
Edit: replaced '*' with