On most networks, you will have no way to know if someone did a /whois on you unless you are an IRCOP. The request doesn't go to you... it goes to the server and then back to the requester.
And for the removing mIRC's version response, you are not supposed to do so except by disabling all ctcp replies to everyone or to specific nicks. You won't be able to hide mIRC's reply and put in your own reply. We can't help you to do that here, per the rules.