Witty post! To answer your first question, you mention the promo code to your travel agent, and they get it added to your itinerary. I believe the reason this is required even though the event is complimentary is that it lets Regent manage capacity, similar to the complimentary excursions and specialty dining reservations.
For your question about the specific entertainment on your cruise, I think you'll get more information on the roll call thread for your cruise. Here's the link to the Spotlight on Hollywood October 3, 2022 roll call: https://boards.cruisecritic.com/topic/2828907-mariner-october-3-2022.