In English language terms for family relationships, there is no relationship called "nephew once removed." The son of your nephew is your great nephew.
You don't, simple as that. You could say cousins if it's that important, or "my aunt's nieces and nephews on the other side," but there isn't an actual term for that except your "uncle's wife's siblings children."
Your father's great nephew is the son of your father's niece or nephew. Your father's nieces and nephews are your first cousins. Their children are your father's great nieces and great nephews, and are your first cousins, once removed.
Your dad's nephew is your first cousin, his children are your first cousins once removed.
The children of your grand nephew (or great nephew) are your great great nephews and great great nieces (depending on whether they are girls or boys).
Your great nephew is your kids' first cousin once removed.
Your daughter and your nephew are first cousins. His daughter is your daughter's first cousin, once removed.
Your nephew is the son of your sibling and a first cousin of your childrenYour grand nephew (or great nephew) is the grandson of your sibling and a second cousin of your grandsonYour great great nephew (or great grand nephew) is the great grandson of your sibling and is a 2nd cousin once removed of your grandson
Your child and your nephew are first cousins. Your child and your great nephew are first cousins, once removed.
First cousins once removed.
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
Your child and your nephew are first cousins. Your granddaughter and your great nephew are second cousins. Your granddaughter and your great great nephew are second cousins once removed
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.