I would say do the following:
First find that hub you are talking about, you can use the search for that, when you have found the hub then open it.
Once that hub is open look on the right side and you will see that person's profile image and name. Now click on either the profile image or name and it will take you to that person's hub site.
Then once you get on that person's hub site look to the right side and below the first gray rectangle containing their profile image and name you will see another gray rectangle containing text links and the link below the RSS link is a link where you can ask that person a question directly.
Hope this helps!