"The Meaning of Epignosis." See https://biblicalstudies.org.uk/pdf/eq/1975-2_085.pdf
"Epignosis - 5x in the Septuagint - 1Ki 7:2; Pr 2:5; Hos 4:1, Hos 4:6; Hos 6:6" (Preceptaustin)
Kenneth Wuest: "Knowledge or epignosis is full, perfect, precise knowledge as opposed to gnósis, imperfect, partial knowledge."
Trench's Synonyms of the New Testament:
Of ἐπίγνωσις, as compared with γνῶσις, it will be sufficient to say that ἐπί must be regarded as intensive, giving to the compound word a greater strength than the simple possessed; thus ἐπιποθέω (2 Cor. 5:2), ἐπιμελέομαι: and, by the same rule, if γνῶσις is ‘cognitio,’ ‘kenntniss,’ ἐπίγνωσις is ‘major exactiorque cognitio’ (Grotius), ‘erkenntniss,’ a deeper and more intimate knowledge and acquaintance. This we take to be its meaning, and not ‘recognition,’ in the Platonic sense of reminiscence, as distinguished from cognition, if we might use that word; which Jerome (on Ephes. 4:13), with some moderns, has affirmed. St. Paul, it will be remembered, exchanges the γινώσκω, which expresses his present and fragmentary knowledge, for ἐπ ιγνώσομαι, when he would express his future intuitive and perfect knowledge (1 Cor 13:12). It is difficult to see how this should have been preserved in the English Version; our Translators have made no attempt to preserve it; Bengel does so by aid of ‘nosco’ and ‘pernoscam,’ and Culverwell (Spiritual Optics, p. 180) has the following note: ‘Ἐπίγνωσις and γνῶσις differ. Ἐπίγνωσις is ἡ μετὰ τὴν πρώτην γνῶσιν τοῦ πράγματος παντελὴς κατὰ δύναμιν κατανόησις. It is bringing me better acquainted with a thing I knew before; a more exact viewing of an object that I saw before afar off. That little portion of knowledge which we had here shall be much improved, our eye shall be raised to see the same things more strongly and clearly.’ All the uses of ἐπίγνωσις which St. Paul makes, justify and bear out this distinction (Rom. 1:28; 3:20; 10:2; Ephes. 4:13; Phil. 1:9; 1 Tim. 2:4; 2 Tim. 2:25; cf. Heb. 10:26); this same intensive use of ἐπίγνωσις is borne out by other similar passages in the N. T. (2 Pet. 1:2, 8; 2:20) and in the Septuagint (Prov. 2:5; Hos. 4:1; 6:6); and is recognized by the Greek Fathers; thus Chrysostom on Col. 1:9: ἔγνωτε, ἀλλά δεῖ τι καὶ ἐπιγνῶναι. On the whole subject of this § see Lightfoot on Col. 1:9.
1 Cor. 13:12 is certainly a verse to ponder.