command to determine where domain is hosted
 

Is there a linux/unix command that will return where a domain is hosted at? Basically, the command that is used for whoishostingthis.com?

no

but there are other ways..
quite simple too (to see who is actually providing the dataservices/upstream for the domain:

do a ping to the domain, fetch the IP address
or do a nslookup the reverse record associated with the ip address.
(e.g. a domain can be bonded to an IP address, which itself is officially bonded to another (sub)domain.
since the ipaddress is not owned by the domain host itself, but by the provider.

then go to (for europe based addresses):

http://www.db.ripe.net/whois?form_ty...&submit=Search

or go to (for american bases addresses):
https://ws.arin.net/whois/

or go to (Latin American / Caribbean addresses):
http://lacnic.net/cgi-bin/lacnic/whois

or go to (Asia / Pacific addresses):
http://wq.apnic.net/apnic-bin/whois.pl

or go to (African addresses):
http://www.afrinic.net/cgi-bin/whois

in either of these search engines, type the ip address, and it will come back with a result.
(if it's found in the database, if not, you need to go to another search from the one i mentioned)
the result should contain a netblock/inetnum (pool of ipaddresses, a.k.a Assigned PA/PI space)
and address information.

good luck