Hi
I've been trying to force showing captcha, but had no luck, so I've disabled our template to make some tests and even while using default joomla template captcha is not showing in ask a question or in vm registration. I think it has not been implemented or there is some missconfiguration in VM settings. Unfortunately I'm not VM expert so I do not know how this has to be configured. I think it would be better if You ask them directly or look into their documentation.
From what I've found online there should be an option to enable/disable recaptcha on ask a question (if You have the latest version of component). Unfortunately I could not check that myself since I only received FTP access and not joomla panel access.