Either they are second cousins or technically not related at all. Your cousin's niece would be one of her siblings' children, in which case it would one of your cousin's daughters, or her spouses' niece, in which case there is no blood relationship, but most families would refer to them as a cousin.
Your daughter and your niece's children first cousins, once removed.
Your niece and your daughter are first cousins.
Your daughter and your niece's daughter are first cousins once removed.
Your daughter and your niece are first cousins to each other.
Your daughter is your brother's niece. Your brother is your daughter's uncle
my great grand-daughter
Your wife's niece is also your niece, and her daughter is your great niece. It is to be hoped that you do not have a relationship WITH her, merely TO her.
Your brother's daughter is your niece and his granddaughter is your great niece.
Since your niece is your daughter's first cousin, your grand niece (the daughter of your niece) is your daughter's first cousin, once removed.
great niece
Your sister's daughter and your sister's brother are niece and uncle to each other. The daughter is the niece of the brother and the brother is uncle to the daughter.
First cousins once removed.
She would be your niece. and you would be her uncle.
Your sister's daughter is your niece. Your niece's husband is not related to you.
Your niece's daughter is your great niece. You are her great aunt or great uncle, depending on your sex.