This is another Greek word used by Jesus that has come down to us without ever having been translated is Métanoïa. Nor, like the other two, can it be adequately translated into English. We just have to try to seek out the meaning Jesus intended.
In Thomas it is used only once, at the end—a culmination—of logion 28:
then they will transform their Knowing.
However Jesus uses it quite frequently in the N.T. Gospels, and it is also used in the O.T.
The problem in studying those examples is that when Jerome translated the early Greek texts of the N.T. into Latin he used the term poenitare = to feel sorry. He had some justification for doing this, for in several contexts, specially in the O.T. and as used by John the Baptist, it can carry the meaning of 'penitence, feeling sorry, feeling pain or regret' (Nicoll p.93). Thus it is used for repenting for misdeeds or evil ways, or repentance by sinners.
Maurice Nicoll is the foremost writer on the meaning of Métanoïa. He has a whole section in 'The Mark', with four chapters considering different aspects of its use in the N.T. Gospels. In the first he spells out that it is a compound word, the first half meaning a transformation—not merely a change. And that this transformation results in something fundamentally different from what went before.
The second half of the word derives from the Greek NOUS, which means mind. Hence the 'word Métanoïa therefore has to do with transformation of the mind in its essential meaning' (p.93). He goes on, with extensive discussion and examples, to develop the theme 'A new mind means an entirely new way of thinking, new ideas, new knowledge, and a new approach to everything in life'.
Now, because Nicoll was a scientist (a psychologist who had learnt much from Carl Yung) he sees this transformation to be a task of the mind, for thinking. In the end that is a matter for the intellect and hence for understanding. However, he did not of course have Thomas, and nor is there elsewhere the concept that in Thomas there are three levels of significance of the concept of knowing, and that the highest of these is a Knowing-for-certain that is the antithesis of believing.
This sort of Knowing is something that happens at a higher level than the mind, it is something that happens deep within oneself. It is not an understanding, it is an awareness and a conviction.