Whether the fact that the existence of emptiness, of emptiness is actually whether is that known by the mind that sees emptiness. Does the mind that knows emptiness, know that emptiness exists? Those are difficult questions in a way. But if one is asking, do I know emptiness? Obviously one does not know emptiness. You only know that you know emptiness when you know emptiness. You know that you know emptiness only when you really know emptiness.

-- 4th Zong Rinpoche, Tenzin Wangdak