Is it possible to use CirrusSearch to search (the topic pages of) a particular talk page that uses Structured Discussions (like this one)? I.e. restrict search results to only topics from that talk page.
Topic on Help talk:CirrusSearch
No.
Unfortunately, it’s not possible to search Structured Discussions pages using CirrusSearch at all, with or without constraining the search to a particular page. This is one of the many reasons for which Structured Discussions is deprecated and to be replaced with DiscussionTools.