Depends whether your father is dead or alive.
And, there seems to be some family "issue" here, ie why has your nephew got your father's will?
If your father is alive and he has made a will then it is no business of yours or anyone's until he dies. So, in this case forget it!
If your father has died and you cannot get his will from your nephew then, if the will has been probated, go to the Court where that was done and ask the Court for a copy of it.
Some more information would still be helpful here though.
And, the obvious answer to your query (whn i first saw it) is "Ask for it from your nephew" or "Ask your father for a copy of that which he has given to your nephew".
cousin
You are his first cousin.
Your fathers brothers are your uncles. You are their nephew, or niece.
As far as I can make out, Your daughter is your fathers (common ancestor) grandchild, and your grand nephew (not great nephew) is your fathers great grandson. According to the chart at http://freepages.genealogy.rootsweb.ancestry.com/~gentutor/chart.html this would make your grand nephew, your daughters First Cousin once removed
dogs don't really have "families" like people do. a dog may have many fathers. Dogs have no sense of being "cheated on" like people do.
Your nephew's nephew is the son of one of your nephew's brothers or sisters. He is your great nephew.
Your mother's (mom) nephew is your answer.
Your nephew's son is your grand nephew or great nephew.
Your nephew's son is your great nephew. Your niece's son is also your great nephew.
Your wife's nephew is your nephew and his son is your wife's, and your, great nephew.
The male counterpart of a niece is a nephew.
Niece would be an opposite as a niece is female and a nephew is male.