Public Class Form2
    Inherits System.Windows.Forms.Form
    Private m_Woher as System.Windows.Forms.Control
    Public Property Woher as System.Windows.Forms.Control
        Get
            return m_Woher
        End Get
        Set(Value as System.Windows.Forms.Control)
            m_Woher = Value
        End Set
    End Property
    ...
End Class

Dim frm as New Form2
frm.Woher = sender
frm.ShowDialog()
...

me.Woher.Name