What is the expiation for kissing a foreign woman on two different days in Ramadan while fasting, and is it necessary to make up for one day or for each day?

You must take the initiative to repent to Allah and increase your prayers for forgiveness for committing the sin and violating the sanctity of the holy month. If your action did not result in the emission of pre-seminal fluid (madhy) or semen (maniy), then all that is required of you is to seek forgiveness and repent. However, if it did result in the emission of semen or pre-seminal fluid, then you are only required to make up for the fast. If you need to make up for two days, you must make them up each day separately, and fasting one day does not suffice for both.