In Theaetetus, when asked about knowldegde (ἐπιστήμη) he first suggest that knowldege is perception (αἴσθησις). Just before, he says the following :
δοκεῖ οὖν μοι ὁ ἐπιστάμενός τι αἰσθάνεσθαι τοῦτο ὃ ἐπίσταται
The translation of Harold N. Fowler is the following :
I think, then, that he who knows anything perceives that which he knows
As in the french translation I have, there is in english a very interesting ambiguity : does he knows because he perceived that which he knows ? Or does he actually perceives the fact that he knows i.e. perceives that he is knowledgeable ?
From my understanding of the pronoun οὗτος, the ambiguity comes from the greek itself. Is it correct?
Edit : This ambiguity is better put as question of temporality, in which, if I'm not mistaken, both interpration of "that" are demonstrative : Does he who knows, knows because in the past, he perceived something ? Or does he who knows, in the present, perceives his knowledge ?