Can you tell me about a customer who you found difficult to understand and how you approached that interaction?
In this scenario, I would try not to start the conversation about the complaint. I will let the customer tell his or her say about the problem even if I know what he is gonna say next. I will be a good listener at that time and will use that opportunity to build togetherness.
Note: You should know the answer to this question very well if you are an experienced person since it is commonly asked in the customer service representative interview questions.