What is the expiation for someone who fondled his wife during the daytime in Ramadan, leading to seminal emission, and then continued fondling until he had satisfied his desire?

You must repent and seek forgiveness for violating the sanctity of the revered month and invalidating the fast. You are obligated to make up for the day on which ejaculation occurred without vaginal intercourse, because the fast was invalidated by the emission of semen. There is no expiation (kaffarah) upon you, according to the majority of scholars. The Malikis held that expiation is necessary for intentionally causing semen to be emitted through kissing, direct physical contact, or foreplay, but the preponderant view is that expiation is not required.