I’ve seen (in the romaneto “Gerda malaperis”):
Kion vi volas diri?
However, I suppose that just like in English, there is a slight difference between “What do you mean?” and “What do you want to say?”. The former asks about the meaning of that which the speaker said, while the latter (though it may also have the same meaning) may be understood as “Please change your way of expression because I didn’t understand what you said.”
I find the same distinction made in Bulgarian: „Какво имаш предвид?“ and „Какво искаш да кажеш?“
So, how can one say that in Esperanto? Does “Kion vi signifas?” convey the same meaning or this won’t work?
Or am I being too picky and there is no difference?