The phrase "simple question" means asking something that does not require a complex or complicated answer. It's something that can be easily answered or understood without much difficulty. Full definition
A short survey is given to clients which asks a few very simple questions about their pet. (ahna.net)
Start by asking simple questions of clients about their sales in the past quarter, the number of returning customers and expectations. (entrepreneur.com)
Most people can't answer simple questions like whether they can take their pensions with them if they change jobs. (moneysense.ca)