title_body: Can I keep a reading diary on my device?
upvoted_answer: You can not directly keep a diary on your device of your written reviews. If that is your question. You can indeed write your review on the device after finishing the book. And you can always find it online on the Kobo.com website.
  
  What is maybe an option but rarely used, is to make a screenshot of your written review. This can be done by editing the code of your device a little bit. More of the explanation about that can be found in this question: Is it possible to take a screenshot from a Kobo ereader device?
  
  If you can categorize your annotations that would also be an option to annotate your review stuff and divide it for annotations of the specific passages in the book and annotations for the review parts in the book.