Your granddaughter and your grandniece are second cousins or third cousins to each other
Your granddaughter and your second cousin are second cousins, twice removed, to each other.
Your niece and your son or daughter are first cousins. That would make your niece and your grandchild first cousins once removed. Your niece's child and your grandchild are second cousins.
Your uncle's granddaughter and your child are second cousins.
Your granddaughter and your niece's son are second cousins.
Your granddaughter and your sister's grandson are second cousins.
Your son and your sisters child are first cousins. The granddaughter is out of synch by a generation. That will make them first cousins once removed.
You would be 2nd cousins, assuming that the brother's wife's granddaughter is also the brother's granddaughter. If the granddaughter is not the granddaughter of the brother, there is no relationship.
Your grandson and your sister's grandson are second cousins to each other.
Your granddaughter and grand niece are second cousins to each other.
Your 1st cousin's granddaughter would be your daughter's niece.
You and your father's cousin's granddaughter are 2nd cousins once removed.