Friend: what is it to know oneself?

Reply: It is knowing oneself as not-knowing. An open field of knowing not-knowing. An ever deepening and expanding not knowing that has no borders, no target and nothing to attain.
First, you let go of all your old knowledge. Your beliefs and opinions are seen to be empty.
You realize the reality of Awareness. Its non phenomenality is revealed as your very Self and the ground drops from beneath you as the vastness of Being/Awareness becomes your experience non-experience.
The mind dissolves in the vastness and you find yourself as the not-knowing that is free from seeking, free from the sense of lack and full of wonder and blissful Being-not-knowing.