What is the ruling on a wife who attends seminars and lectures without her husband's knowledge and consent?

A woman is not permitted to leave her husband's home except with his permission. The fundamental principle is that women are commanded to remain in their homes, as Allah Almighty says: "And abide in your houses," and as the Prophet, peace and blessings be upon him, said: "The woman is 'awrah (private/object of concealment); if she goes out, Satan beautifies her in the eyes of men. The closest she is to the mercy of her Lord is when she is in the bottom of her house." As for what is absolutely necessary for her, such as going out to earn sustenance if her husband becomes destitute, or to a doctor for treatment, or to consult a jurist if her husband does not suffice her in seeking knowledge, then it is permissible for her to do so.