I have seen many explanations of “knowledge” and what it is to “know”, but this seems to be the best way to put the difference between Knowability and Witness-ability. I have a high regard for Avtar Singh… I think his thoughts are well rounded and deep in their meaning!
Un-know-ability does not mean un-witness-ability.
Unknowable exists only relative to the frame of reference of the ego that wants to know it all. As long as there is a desire (of the ego) to know it all, there is un-knowable. When ego dissolves, the unknowable becomes witness-able or the object of awareness of the egoless awakening.
Nature has not created anything that is not witness-able and experience-able by the fully conscious mind. Assuming the ultimate un-know-ability, which is nothing but an artifact of the unconsciousness of the ego, is selling short the wonderful design and dignity of nature and the universe.
Genuine science and genuine spirituality are not two different pursuits. So long as the TRUTH is One, its realization or path to its wisdom is also One. One can argue separation of the mainstream (materialistic only) science from spirituality, but the consciousness-integrated science (Holistic Relativity) is no different than the wisdom of the Buddha, Christ, and Nanak.