Answer:
looking for other books that share the same topic
Step-by-step explanation:
The theme of a book is the subject that will be developed during the narrative, that is, it is the main subject that will serve as a basis for a story to be told. This theme can be family, friendship, depression, abandonment, solidarity, overcoming, among others.
Books that share the same topics are usually connected by the same theme. For this reason, if Denis wants to find the theme of the book he is reading, he can search for books that share the same topic to facilitate his search.