This is the 11900th most frequent Polish word.
książce
"książce" means "to the book" or "about the book" in English, depending on context.
The word 'książce' here is used in the locative case, indicating the location of the content being read.
Czytałem przed chwilą fragment o historii w tej książce.
I was just reading a passage about history in this book.
In this context, 'książce' is again in the locative case, showing where the action of reviewing the notes is focusing.
Muszę jeszcze raz przejrzeć notatki w mojej książce.
I need to review the notes in my book one more time.
Here, 'książce' is used in the locative case, indicating the topic or focus of the conversation.