The other side might be able to understand the answer but would not know the question.

How could he have known the question that so haunted her?

"We may never really know the question that is on anyone's mind: Why did they do this?"

"We're at a point where intelligence services might not even know the question to ask," he added.

The only problem is that we don't know the question.

He knew the question, and unfortunately the answer was no.

The guest doesn't know the question behind that number in advance.

You know the old question, What if they gave an election and nobody came?

Others know the question but fear what the answer will mean.

How did she know exactly the right question to ask?