Any subject that encourages a student to discuss how she feels about a class or subject can be used as an expository topic. One such topic is "What is your favorite class in school, and why is it your favorite?" Another topic might be "Name one thing that you would change about your school and describe how you would change it." Expository topics can be framed as questions or sentences.
Expository topics about family are very useful; everyone has a family, so it's a subject that everyone can use. Some good examples of topics include "What is the thing you love most about your family and why do you love it?"; "Who do you think is most like you in your family and what makes you like them?"; and "Do you think your family is different from other families? What makes your family different?"
Expository topics about individuals are useful because they encourage students to think about themselves. Some specific topics include "What makes you different from everybody else? Do you like that about yourself?"; "Who do you admire most and why do you admire them?"; and "What is the one thing you want to do most before you die. Why do you want to do it?"
It is always interesting and fun to write about things that will never happen. It also helps the student to develop an artistic quality in his writing. Some fun things to write about include "What animal would you like to be and why?"; "What inanimate object are you most like and what makes you similar to that object?"; and "What color describes you and why?" Topics like this can give your students the opportunity to be creative in their writing. The topics will also help your students see writing as a fun activity and not a chore.