Hi everyone,
'Knowing oneself' is such a complex matter that every individual will understand it in his/her own way.
I understand it as becoming aware of the subject that sees and experiences all of life. Through a process of Neti Neti (not this...not this) that was mentioned in the thread on 'Tat Tvam Asi', ... we arrive at the subject that is the final observer.... always observing but never observed.
After all life's experiences, after all sorrow and desires, after all successes and failures, after all duties and responsibilities, after all questions and theories, after all rituals and prayers, after all meditations and mind control...we finally arrive at the centre, the light within....the true Self.
Once we experience that, everything else falls away as an illusion.....only the Self remains. This is what according to me, the 'Know Thyself' refers to.
Cheers.
Sriram