what do you mean + a clause

Question

Person A says, "Nobody can reach the top of the mountain."

Person B responds,

What do you mean by saying nobody can reach the top of the mountain?

What do you mean when you say nobody can reach the top of the mountain?

Both of them are correct and common. But is the following sentence correct? I hardly ever see it.

What do you mean nobody can reach the top of the mountain?

Answer 1

As that sentence is a direct quote, you should punctuate it with quotations marks:

What do you mean “nobody can reach the top of the mountain”?

That would be correct, but it would be better to say 'mean by "nobody..."'.