There are plenty of obscure interview questions out there — from Facebook's time test to Elon Musk's geography riddle.

But for interviewing veteran John Ryan, he prefers to keep things simple. So simple "you could Google a lot of them," he says.

After all, the question is just a small piece of the puzzle: It's really about getting to the answer behind your answer, according to Ryan.

"I usually ask three whys on whatever question I ask," Ryan, who is president and CEO of leadership development body, the Centre for Creative Leadership, told CNBC Make It.

That could range from "what are you reading?" to "what are your hobbies?"

It's a technique inspired by nuclear science, said Ryan, and it's one designed to see if candidates have one of his most highly prized skills: Curiosity.

"That's what they train you to do in nuclear power, and then you have the real answer. If you ask three whys on whatever the question is that you ask, you find out whether they really, truly, have a curiosity," said the former U.S. Navy vice admiral.