Core Insight:
According to Osho, you know it is true witnessing when nothing remains to witness - only silent awareness without objects. Anything you can observe (even the thought, "this is pretense") belongs to mind; simply witness it and do not identify. Witnessing itself cannot be witnessed. Persist in disidentifying - hand, feelings, thoughts - using the simple test: the object of my knowing is not me. When all objects fall away, the witness alone remains.