Aññā: ‘highest knowledge’, gnosis, refers to the perfect knowledge of the Arahat Saint; see: ariya-puggala. The following passage occurs frequently in the Suttas, when a Bhikkhu indicates his attainment of Nobility arahatta: He makes known the highest knowledge aññam vyākaroti, in exactly this way: ‘Rebirth has ceased, fulfilled is this Noble life, done is what should be done, and there is no more of this to come.’
The ‘ability of highest knowledge’ aññ indriya = aññā - indriya; see: indriya, however, is present in six of the eight stages of Nobility, that is, beginning with the fruition of Stream-Winning sotāpatti - phala up to the path of Nobility arahatta - magga. See Dhs. PTS 362-364, 505, 553; Indriya Vibhanga; path 162.