If you mean the where the email came from then you need to look though the mail headers...tends to be a compromised machine sending them.
If you mean the actual URL they want to try to trick you into clicking. You can go to one of the domain registers and run whois. Networksolutions is one of the largest but there are others for other countries.
All you will generally find is fake information. You could try the ip address and look that up in the ip registry like arin but most likely all you will find is a hosting center. Or it could all map back to a country like china where you will be able to find nothing.
From time to time, I receive spoof or phishing e mails from people or "companies" purporting to be someone they are not. The other day, I received one from "Amazon", and I know it was not the real Amazon
Somewhere I read that you can reverse look up these url's to see who this is. Is that so? If so, do you know who it is? I know there are pay look up sites out there, but I think there is a free one also. Thank you!