Your second cousin's nephew is your second cousin, once removed, if the nephew is a child of the second cousin's sibling. Your second cousin could also have a nephew who is the child of a sibling of the second cousin's spouse. In that case the nephew is not related to you.
Your cousin's nephew is the son of your cousin's sibling.
Your first cousin's nephew is your first cousin, once removed.
Your second cousin's nephew is your second cousin, once removed.
The nephew of your first cousin, once removed, is your first cousin, twice removed.
The nephew of your second cousin, once removed, is your second cousin, twice removed.
And so forth...
The only way your uncle could be your nephew would be if your sister or brother had a son with your grandfather or grandmother. Aside from being culturally unacceptable and illegal, it is highly unlikely ever to happen.
One way a cousin could also be your nephew is if your sibling married a cousin and had a son. As the son of your sibling, he is your nephew. As the son of your cousin, he is your cousin, once removed.
Your first cousin once removed is the child of your first cousin or the first cousin of one of your parents.
To your uncle, you are his niece or nephew.
Your uncle's nephew could be you (if you are a boy), or your brother, or your first cousin. Your uncle's nephew could also be unrelated to you if he is the son of a sibling of your uncle's wife.
You are your nephew's uncle, or aunt, and his son's great uncle, or great aunt. Your nephew's son is your great nephew.
You would be a neice or nephew, neice if a girl and nephew if a guy.
You are a great great Aunt (or Uncle) to the grandson of your Nephew.
Your brother's (or your sister's) son is your nephew and you are his aunt if you are a female or his uncle if you are a male.
An uncle's nephew and the uncle's child are first cousins to each other. The uncle's great granddaughter and the nephew are first cousins twice removed to each other.
You are the grand uncle to any children your nephew or niece have.They would be your grand nephew or grand niece.If the children of your nephew/niece have children of their own, you'd be a great uncle too.
A great uncle is the brother of the great nephew's grandfather or grandmother.
If you are male and you have an uncle, you are that uncle's nephew.
'Niece' is what a little girl is to her uncle. 'Nephew' is what a little boy is to his uncle. The children also are the niece and the nephew of their aunt.
You are your nephew's uncle if you are male, and his aunt if you are female.