Is it permissible for a Muslim father to attend the wedding of his Christian daughter who married a Christian man?

We praise Allah for guiding you to Islam, and we advise you to be dutiful to your daughter and invite her to Islam. You have no guardianship over her marriage to a non-Muslim, as Al-Shafi'i and Ibn Taymiyyah stated that guardianship is severed by the difference in religion. It is not permissible for you to attend her wedding ceremony if it involves forbidden acts such as ostentatious display (تبرج), mixing of sexes, and drinking alcohol.