Is it permissible for a wife to suck her husband's penis? And is her request considered an audacity that necessitates divorce?

The wife erred in her request, as this act is disgusting, contrary to good taste and human nature, and may lead to contact with impurities. Do not divorce her merely for this request, for her intention might not have been bad, or she might have thought she was pleasing you thereby. So, explain the Islamic ruling to her, nurture her in religion, and keep her away from anything that leads to such thinking, like pornography. Divorce is reprehensible unless there is a need for it, and it can be forbidden because it causes harm without necessity.