Yoga yields relative truth, i.e. true from a particular viewpoint, not ultimate truth.

When one inquires who is the experiencer of the three states, one does gets soul ,which is the innermost self . The innermost self is in the form of consciousness. Thus the formless  consciousness is  the knower or  witness of the three states.The consciousness is real  eternal.

Yoga cannot yield non-dual truth because everything that yogi does or practices and experiences within the ‘known.' Yoga yields relative truth, i.e. true from a particular viewpoint, not ultimate truth.

Man and all the objects of the world within the waking or dream are known and passing away every moment, hence unreal. Hence we ought not to get attached to the passing show. Not only we individuals will change and die, but empires and mountains and the population will disappear with the waking or dream.

Seeker has to start with mind which is the matter. He has to analyze mind and taking away from it all those portions which are ever changing or passing, he gets at the formless witness of the ever-changing.

When a seeker is able to make the distinction between formless witness and the three states then he be able will understand the fact that what is truth and what is untruth. The soul/self/sprit is present everywhere in everything in the three states.  

There are two factors to remember:-the knowing capacity and that which is known. The three states are known, and they are all passing away and are therefore unreal. Without the knowing capacity i.e. the knower/witness in existence there could have been no such thing as knowing these things.  Knowing implies two factors, the knower or the knowing capacity, or that which becomes aware; and the known. Without these two factors one cannot use the word know.

The known [three states] always passes away. When one is able to distinguishing between knower and known, he becomes aware of the fact that the subject is the formless knower and object is the waking/dream, which is full of forms and shapes. When waking and dream disappears, the soul/self alone prevails as eternal existence.

The nondual truth is always real. Reality does not exist with forms and names and feeling. That which underlies these is the reality. Reality underlies limitations, being itself limitless. Reality is not bound. Reality underlies unrealities, itself being real. Reality is that which is. Reality is as it is. Reality transcends speech. Reality is beyond the expressions `existence, non-existence.

The reality which is the mere consciousness that remains when ignorance is destroyed along with knowledge of objects, alone is the Self [soul]. In that nondual real form of the Soul, which is abundant Self-awareness, there is not the least ignorance.