What is it that makes it evident that you are, that you exist? What is it that makes it impossible to deny that you are?
Is it presence of thoughts? Are these seeming patterns of language what you are? Are you authoring thoughts? Are passing thoughts indicative of your true nature?
Is it the presence of a body? What is the body? How do you know of the body? Isn't the "body" just a concept used to talk about the various sensations and perceptions (appearances)? Something seems to be there, yet it's a creation of concepts only - the "body" cannot be known unless these sensations are all taken together. The passing sensations and appearances are all bundled together into a concept called "body".
The sensation called "breathing" is taken as "I am breathing." Then "I am this body and I am breathing." "I am moving this foot - this is my foot."
If we lay aside the conceptualization and be brutally honest, these are all just appearances and we don't have any idea what they are. They are conceptualized using acquired knowledge.
And these appearances register right on this consciousness, right HERE - the wall "over there" and the "foot"-sensation and the "breathing"-sensation and the "nose"-sensation... these are appearances, "objects", appearing TO YOU.
If a thought comes and then a feeling or emotion, that's more sensation, more appearance, more "objects" appearing TO YOU. Just notice all the sensations appearing and how the thoughts conceptualize them into a "ME" and "MINE". Notice how the thoughts create the assumption/illusion of "that" being "over there" and "this" being "in here".
Notice this story of "ME" has always been about these sensations, has always been a story about something appearing.
Nothing that appears is what you are. Neti-neti, not this, not that. And it becomes clear that EVERYTHING appears this way, right here on this Consciousness. Even the idea of consciousness appears as a "thought"-sensation.
The only "thing" we cannot eliminate in this way is stillness, silence, that which is not a "thing" appearing yet cannot be negated. All comes out of this stillness and silence and returns to it. All appears IN this stillness and silence.
This is very simple and obvious, once the compulsion to conceptualize everything is suspended. And it just takes a moment - just pause thought, pause the conceptualizing for one moment. Be still.
You do not change. You do not appear. Yet you have to be there for anything to appear. This immediately burns up all identification, as it becomes obvious that nothing appearing, as relative appearances, is what you are. Nothing can be gained, attained, lost, nothing is born or dies, nothing appearing has any absolute and separate existence.
What you are can never be found, yet is absolutely undeniable.
How do you know yourself? Are you an appearance or THAT FROM WHICH appearances come and go?