Argument not optional error while passing value of variable between subs

You'd better start simple:

Sub Test1()
   A_Test2 application.CountIf(range("DE_Co"), "<>-")
End Sub

Sub Test2(iRowdata As Integer)
   c01= Names("DE_InputRange").RefersToRange.Resize(iRowdata).address
End Sub

next step

Sub Test1()
   x=application.CountIf(range("DE_Co"), "<>-")
   A_Test2 x
End Sub

Sub Test2(iRowdata As Integer)
   c01= Names("DE_InputRange").RefersToRange.Resize(iRowdata).address
End Sub