The book being repaired by Dewey Denouement in the sub-basement is "Introduction to MacGuffins." A MacGuffin is an object that is desired by and serves as motivation for characters in a story but is ultimately worthless, or unexplained to the reader/viewer. A prime example in the books: the sugar bowl. However, the show changes this when Kit Snicket reveals the contents of the sugar bowl in The End (2019).
The hotel is, fittingly enough, called the Hotel Denouement. Denouement is a word, which in this case, means the final part of a play, film, or narrative in which the strands of the plot are drawn together and matters are explained or resolved.
In the first part of Penultimate Peril, Carmelita Spats says she wants to go to Littlest Elf Land. This is a reference to the 2004 movie of the same name, where said book is mentioned a few times.