I will often expose them to my thought process on solving the question. Especially when my class has a smart board with internet access, I will admit that I don't know, but show them that the important thing is understanding where to find the answer.
That is a great response and what I do myself. I have students from many different cultures and parts of the world, we're a very diverse group. Sometimes the language spoke, tone and accent hinder me from hearing a question or understanding the full context of what they are asking. Having them repeat it or rephrase it followed by telling them I am not sure what they are asking seems to be the best approach and together we can figure out the question/answer.
I would ask the student to repeat the question or I may even repeat the question to be sure of what the student is asking.
I may also say, I am not sure of what you are asking.
I usually will ask the student to ask me the question again but this time also include an example. By asking in this fashion I hope that the example will enlighten the question.
