ñāṇadassana-visuddhi:'purification of knowledge and vision',is the last of the 7 purifications and a name for path-knowledge (maggañāṇa),i.e.the penetrating realization of the path of Stream-winning,Once-returning,Non-returning or Arahatship.Vis.M.XXII furnishes a detailed explanation of it (s.visuddhi,VII).
In A.IV,41 ñāṇadassana apparently means the divine eye (dibbacakkhu,s.abhiññā),being produced through concentrating the mind on light.