What is the ruling on a wife raising a knife to her husband's face to demand a divorce from him?

It is not permissible for a woman to seek divorce from her husband without a legitimate Shar'i reason. Her threatening her husband with a knife is an impermissible act and constitutes defiance (nushuz). Allah has granted men guardianship over women, and the Qur'anic verse enjoins treating defiance with admonition, boycotting, and light striking. The Prophet (peace be upon him) also forbade terrifying a Muslim by pointing a weapon at his brother, and this applies even more so to a husband.