The book doesn't explicitly state what Jem likes studying in the 6th grade. However, we can infer some of his interests based on his personality and the events in the story:
* History: Jem enjoys learning about the past, as seen when he reads about the history of Maycomb and the events leading up to the Civil War.
* Nature: He is fascinated by the natural world and enjoys exploring the woods and observing animals.
* Justice and Morality: Jem shows a keen interest in issues of right and wrong, as evidenced by his strong reaction to the trial of Tom Robinson.
However, it's important to remember that Jem is a young boy and the book focuses more on his experiences outside of the classroom than his academic interests.