In the Interact Pane of a Watch Now room, there is the option to Ask a question.
Depending on whether the room is Moderated or not, the questions asked will either appear in the Interact Pane, or get sent to the Moderator for approval.
Approved questions will appear in the Interact Pane. Here, you can upvote questions by clicking the thumbs up button. Moderators can also answer your questions via text response if they are not answering Q&A on the live stream.