The Data ONTAP PowerShell Toolkit wraps the Manage ONTAP API. Remove-naquota is basically quota-delete-entry..
The * is a wildcard for "default". To delete a specific quota use the type, the qtree path, and the volume
PS C:\> remove-naquota tree /vol/vol1/qt_test vol1
Now let's add a user quota to qt_test
PS C:\> add-naquota user /vol/vol1/qt_test vol1
New let's delete it:
PS C:\> remove-naquota user /vol/vol1/qt_test vol1
Since this is a quota on a specific tree and not a default, I use the parameters <type> <qtree path> and <volume>. Type can be tree, user, or group. The type must match the type of quota it is.
Does that help?