Then Vakaknavi said: 'Venerable Brahmanas, I shall ask him two questions. If he will answer them, none of you, I think, will defeat him in any argument concerning Brahman.' Yagnavalkya said: 'Ask, O Gargi.'

In plain words: Gargi, also called Vakaknavi, tells the other Brahmanas, the priests, that she will ask Yagnavalkya two questions. If he answers them, she says, none of them will beat him in debate about Brahman, the ultimate reality. Yagnavalkya invites her to ask.