If a person's soul get liberate(Jivan Mukta) and alive, then does his knowledge is equal to the knowledge of brahman?
Yes if we go by the following Mundaka Upanishad verse:
He who knows the Supreme Brahman becomes Brahman Itself. In his family none devoid of the Knowledge of Brahman is born. He crosses over sorrow, he crosses over sin. Freed from the knots of the heart he becomes Immortal.
No, I do not think so.
Because, Brahman is different from Ishvara, the All-Knowing Supreme.
Brahman is Existence-Consciousness-Bliss. Brahman is all-pervading. So who will know whom?
The knowledge is possible only when knower and known are different, which is not the case for Brahman.
As the Kenopanishad says
As Brahman is ear of ears, mind of mind, speech of speech, life of life. the wise men reject the false knwledge of the self (ego) as perceived by the senses and become immortal.
Eyes can not go there, speech can not go there, mind can not go there,None knows Brahman and we do not know how to explain Brahman.He is definitely different from anything that can be known..That what is not expressible by speech but by which speech is expressed, know that is Brahman. That what is worshipped is not Brahman. He who knows Brahman knows that he knows not.He who thinks he knows Brahman does not know Brahman.
So I think all these make my point clear that the question of Brahman's knowledge of anything does not arise.