Your granddaughter and your first cousin are first cousins, twice removed, to each other.
We can't tell, since we don't know exactly what relation your cousin is to you ("cousin" covers a pretty wide degree of relationships), but probably also a cousin of some kind. For example:
If your cousin is your first cousin, then your cousin's granddaughter is your first cousin twice removed.
If your cousin is your first cousin twice removed, your cousin's granddaughter could be your first cousin four times removed or your third cousin, depending on the details.
Your first cousin's granddaughter is your first cousin, twice removed.
Your first cousin is your granddaughter's first cousin twice removed.
Your granddaughter and your second cousin are second cousins, twice removed, to each other.
Your granddaughter and your niece's son are second cousins.
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.
they're your cousins
Your granddaughter and your sister's grandson are second cousins.
Your 1st cousin's granddaughter would be your daughter's niece.
You and your father's cousin's granddaughter are 2nd cousins once removed.
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.
Some of your granddaughter's first cousins are also your grandchildren, others are not related to you at all.
They are first cousins once removed. Your niece's children and your grandchildren will then be 2nd cousins.
Your granddaughter and your first cousin are first cousins, twice removed, to each other.
Your grandson and your sister's grandson are second cousins to each other.