Hi Anu,
Exit interviews are generally used to get honest feedback from employees. They might be the most factual ones because they are taken when the employee leaves the company, and hence the company can work on any shortcomings or improvements required.
I am attaching a sample questionnaire. You can include more questions pertaining to your industry and company. Also, you can add a section where you request the employee to suggest steps for improvement.
Regards,
AJ