Certainly! Here are some examples of security questions that you can use in WHMCS:

1. What is your mother's maiden name?
2. What is the name of your first pet?
3. What city were you born in?
4. What is the name of your favorite teacher?
5. What was the make and model of your first car?
6. What is your favorite book?
7. What is the name of your childhood best friend?
8. What is the name of the street you grew up on?
9. What is the name of your favorite fictional character?
10. What is the name of your favorite movie?
11. What is your favorite color?
12. What is your favorite holiday destination?

Remember, it's important to choose questions that are meaningful to the user but not easily guessable by others. Additionally, you may want to advise clients to keep their answers confidential and not share them with others. This helps maintain the security of their accounts.