If you are logged into your Spacehive account you can find the project creator's email address and contact them directly.
If you have a private question that you would like to directly ask the project creator, then you can do so via email. To do this, you will need a Spacehive account, as only when you are logged in will you be able to see the ‘Ask me a question’ link on their project page (see image below).
If your question is more public interest (i.e. you believe that the answer to it would benefit other people viewing the page) then you might want to consider leaving a message in the comments box at the bottom of the project page.