Is it permissible for a young man who was nursed by his paternal grandfather's second wife to marry the daughter of his father's full paternal uncle from his first wife?

It is not permissible for you to marry your paternal uncle's daughter, because she has become your paternal sister through breastfeeding due to your suckling from your grandfather's wife. Breastfeeding prohibits what lineage prohibits, as stated in the Hadith: "What is prohibited by lineage is prohibited by breastfeeding." A brother's daughter is forbidden by lineage, by consensus, as Allah the Almighty says: "Prohibited to you are your mothers, your daughters, your sisters, your paternal aunts, your maternal aunts, your brother's daughters, and your sister's daughters."