The context menu does not provide which control has been clicked.
Workaround:

Point p;
Control currentControl;
 
void radContextMenu1_DropDownOpened(object sender, EventArgs e)
{
    p = ((RadContextMenu)sender).DropDown.Location;
    TraverseControls(this);
}
 
public void TraverseControls(Control ctrl)
{
    foreach (Control control in ctrl.Controls)
    {
        if (control == ctrl.GetChildAtPoint(ctrl.PointToClient(p)) && control.Controls.Count > 0)
        {
            currentControl = control;
            TraverseControls(control);
        }
        else if (control == ctrl.GetChildAtPoint(ctrl.PointToClient(p)))
        {
            currentControl = control;
        }
    }
}