Every job comes with challenges, including working as a photographer. When the interviewer asks this question, they care less about what the actual problem was and more about how you solved the issue. The only time they will give more than basic care about the challenge is if you faced something very unusual. Then their ears will perk up, otherwise, they will only care about how you faced your challenge. Be prepared with an example and an explanation.

"The most challenging part about being a photographer is making sure the client understands their own needs. Very often, clients know that they want photos taken, but have not spent time planning what kind of shots they want. Of course, this affects pricing and time, but they haven't thought that far ahead. To compensate for this issue I have been meeting with clients in person, or over the phone to discuss all details. I quote them a price, and make sure everything is squared away before the shoot."