question How can I know the owner of any domain??

Whois data
If whois is under privacy, there's usually contact email anyway which will be forwarded to the owner
If not, visit dimain directly
If not then owner obviously doesn't want to be contacted

Whois, is the only way I think

Try who is free and paid

who is the best place to find this out.

whois privacy makes this difficult now, it even free with most registrars, there may be other paid methods

who.is