Your 1st cousin's daughter is your 1st cousin once removed.
Your daughter's cousin's daughter is a cousin once removed.
its your nephew
Your niece and your daughter are first cousins. Your daughter and the daughter of your niece are first Cousins, once removed.
Your daughter and your first cousin are first cousins, once removed.
If you have two nieces who are not sisters but are each the daughters of your siblings, the two nieces are first cousins. If they each have a daughter, those daughters are second cousins to each other.
Your son and your nephew are first cousins to each other. Their daughters are second cousins to each other.
Your daughter's daughter is your grand daughter. Your nephew's daughter is the granddaughter of your sibling (your brother or sister) The grandchildren of siblings are second cousins.
Second cousins once removed.
First cousins, twice removed. Aunts daughter is your cousin. Aunts daughters daughter is cousin once removed Aunts daughters daughters daughter is cousin twice removed.
They are second cousins
You and your first cousin's daughter are first cousins, once removed, to each other.
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's uncle can be your brother. Her parent who is not your sibling (your brother-in-law or sister-in-law) could also have brothers. They will also be your daughter's uncles, but will not be related to you.
Second cousins