Firstly ask the doubts that you have about the company. Usually, when people go to an interview they research about the company. But they only get the general information and might have some questions regarding the working of the company. I have had such doubts in every interview. So, if you have similar questions, you can ask them. After that, you can ask questions like "What do you think I should improve in or work on?", "What does the company plan to achieve in the short and long term?".