ὁ γιγνώσκων → one who knows, a prudent person, the perceiver

[spiros]

ὁ γιγνώσκων = the perceiver (as opposed to τὰ γιγνωσκόμενα = the objects perceived, Plato, Republic 508e); also ὁ γιγνώσκων, one who knows, a prudent person (Plato, Republic 347d6:  πᾶς ἂν ὁ γιγνώσκων τὸ ὠφελεῖσθαι μᾶλλον ἕλοιτο ὑπ᾽ ἄλλου ἢ ἄλλον ὠφελῶν πράγματα ἔχειν, "any prudent person would choose to be helped by another rather than to have the trouble of helping another")
https://lsj.gr/wiki/%CE%B3%CE%B9%CE%B3%CE%BD%CF%8E%CF%83%CE%BA%CF%89

[spiros]

The point is that further up there is another instance fully written out, so not sure why it has to be repeated in abbreviated form:

ὁ γιγνώσκων = the perceiver, opp. τὰ γιγνωσκόμενα = the objects perceived, Pl.R.508e; also ὁ γ. one who knows, a prudent person

[billberg23]

The abbreviation "ὁ γ." can't possibly be anything but a repeated ὁ γιγνώσκων.  The space-saving abbreviation is there to avoid confusion with τὰ γιγνωσκόμενα which immediately precedes it.