The knowledge about Brahman is known as Brahman Gyan. Here Brahman doesn't mean the creator god Brahma. Brahman means the supreme entity from which all the beings originate, having originated in which all the beings remain and having remained at the end to which all the beings and things merge back into ( as per yatova imani bhutani jayante... Veda verse).
Having knowledge of all the Vedas can make one a pundit but not a Brahman Gyani. Moreover, the true knowledge and meaning of the Vedas is known to none but the Lord Himself (as per vedanta krit vedavid eva chaham... Gita verse).
In Puranas and mythology there have been examples of many Brahman Gyanis. Especially many sages were Brahma gyanis, but I the example of Uddhav I like the most who although was a Brahman Gyani, went on to mature to a next level of realising the supremacy of love for the Lord. Brahman gyana is not the highest level of gyana (although it is accepted as such by some sampradaya and sects) until the gyana of pure unconditional love for the Lord is there.
The Lord is above Brahman (as per brahmano hi pratistha aham.. Gita verse) and Brahman Gyan (as gyan or knowledge comes from Him as per matah smritir gyanam.. Gita verse) and unconditional love for Him is the Highest level.
To be honest, Brahman Gyan is not a thing of expression but personal experience. If the gyani thinks he knows Brahman, then he actually doesn't know It. (as per Kena Upanishad 2.1)