The essence of consciousness is information/experience/knowledge. If consciousness knew nothing it would not be consciousness. So at the very beginning, we can ascertain that consciousness exists by means of knowledge which would also partially be an answer to the question: “How does consciousness exist?”
Speaking about consciousness and knowledge, we cannot claim that knowledge exists, but always the one who knows the knowledge, who is always and only consciousness. This implies that knowledge cannot cause consciousness, but the opposite. I.e. it implies that by way of gaining/causing knowledge, consciousness causes itself by itself.