Participants who have registered for a live Q&A or similar event are not tracked through Show&Tell. Registered participants for a Q&A can be tracked through the service that is being used to host the Q&A event.
Zoom is commonly used by filmmakers for their Q&A. To track and check those who have registered to attend your event, go to your Zoom browser settings and "require registration." You will then be able to customize your registration page and the information that you would like to collect from participants. For more information on using Zoom for a live Q&A read this article here.