Is it permissible for my wife to uncover before my foster father, and what is the evidence for that?

Your foster father is treated like a biological father in terms of the prohibition of marriage to your wife. This is the view of the majority of scholars, and it has even been said to be a consensus, based on the Prophet, peace and blessings be upon him, saying: "What is prohibited by lineage is also prohibited by fosterage." Therefore, it is permissible for him to look at what your wife is allowed to uncover in front of her mahrams, such as the hair of her head, her hands, and her feet.