Your niece's son and your daughter are first cousins, once removed.
Your niece's son's daughter is your great grand niece. Your niece's son is your grand nephew or your great nephew, whichever term you prefer.
Your daughter and your niece are first cousins. Your daughter than your niece's son are first cousin's once removed. Your daughter's child and your niece's child are second cousins to each other.
Your son and your niece are first cousins. Her daughter and your son are first cousins, once removed.
Your daughter and your niece are first cousins. Your daughter than your niece's son are first cousin's once removed. Your daughter's child and your niece's child are second cousins to each other.
Your son and your niece are first cousins to each other. Your son and your niece's son are first cousins, once removed.
Your sister's daughter is your niece. If you are a woman, you are your niece's aunt; if you are a man, you are your niece's uncle. Your sister's son is your nephew.
Your daughter is your sister's niece. Your daughter's son is her great nephew.
Your niece.Your brother's daughter would be your niece and you'd be her uncle or aunt. Your sister's daughter would also be your niece. If your sibling had a son, he would be your nephew.
Your brother's son or daughter is your nephew or niece respectively.
The daughter of your brother is your niece.
Your half-brother's daughter is your niece. Your niece and your son are first cousins to each other.
You are the great aunt/uncle of your sister's son's daughter, and your sister's son's daughter is your great niece.