A definition of Jnana by Shankara
The Brihadaranyaka Upanishad, verse 4.4.20, states the following:
20. It [Brahman] should be realised in one form only, (for) It is unknowable and eternal. The Self is taintless, beyond the (subtle) ether, birthless, infinite and constant.
Here we can see that the Upanishad is stating that Brahman is unknowable. So what of Self-Knowledge or knowledge of Brahman that is so often spoken about? Shankara explains this contradiction in him commentary on this verse:
The knowledge of Brahman too means only the cessation of the identification with extraneous things (such as the body). The relation of identity with It [Brahman] has not to be directly established, for it is already there. Everybody always has that identity with It, but it appears to be related to something else. Therefore the scriptures do not enjoin that identity with Brahman should be established, but that the false identification with things other than That should stop. When the identification with other things is gone, that identity with one’s own Self which is natural, becomes isolated; this is expressed by the statement that the Self is known. In Itself It is unknowable – not comprehended through any means. Hence both statements are consistent.
We can see that Shankara is stating that Brahman is indeed unknowable, and that Jnana, or knowledge, only signifies the cessation of identification with extraneous things, ie. loss of identification with objects, specifically the body-mind. We do not need to affirm our identity as Brahman, as we already are and always have been and always will be Brahman. Any affirmation of Brahman would simply be on the level of thought or concepts, and so it would be Maya, or more ignorance. But once the false identification has been removed, then the Self naturally shines as itself, and this lack of wrong-knowledge, or lack of wrongly identifying as the body-mind, is what is called ‘Jnana’ or ‘knowledge’.
The above is an excerpt from the following post which further explores this topic: What exactly is Jnana (knowledge) according to Shankara and Gaudapada and the scriptures?