You and your first cousin's son are first cousins, once removed.
Cousine
Your granddaughter and your sister's grandson are second cousins.
Your first cousin is your son's first cousin once removed.
Your son and your nephew are first cousins to each other. Their daughters are second cousins to each other.
Your father's first cousin's son is your second cousin. Your father's second cousin's son is your third cousin. If your are asking about your fathers cousins who are in a removed cousin relationship to your father, their relationship to you be more complex, with two different possibilities in each case.
your son and your brother's son will be cousins
your son and your brother's son will be cousins
your son and your brother's son will be cousins
Your uncle's sons and daughters are your first cousins.
third cousin once removed
second cousins to his cousin's children, you'd be third cousins
Your son's child and your nephew are second cousins.