This question actually makes me smile — I love when people want to jump into live book chats. For 'Let's Talk Book', the host info can be surprisingly simple or a tiny scavenger hunt depending on where the show posts its sessions. Usually the person listed as the organizer or credited in the episode description is the one running the weekly live, and that name is what you'll see on the stream title, the event page, or the pinned comment. If the series has a regular lead, they typically open the session, steer the discussion, and introduce any guests.
When I go hunting for the host, I scan three spots first: the platform’s event description (YouTube, Twitch, or Facebook Live), the show's official website or blog, and the social media post announcing the session. I also peek at the chat/mod list during the live; moderators often work closely with the host and their handles clue you in. If the series sends a newsletter, the byline or signature is another clear indicator — I've found the name there more than once when the platform metadata was sparse.
If you want to be certain, join the pre-show or ask in the comments — most communities are friendly and someone will point you to the host or the rotating roster. I usually set a reminder so I don't miss who’s leading the chat, and it makes following up afterward much easier.