public string NewText { get; set; }

Public Property NewText As String

void chartControl1_AnnotationRepositoryChanging(object sender, AnnotationRepositoryChangingEventArgs e) {
  if (e.Change == AnnotationRepositoryChange.Text) {
      AnnotationTextEditingEventArgs textEditingArgs = (AnnotationTextEditingEventArgs)e;
      string newAnnotationText = textEditingArgs.NewText;
      //Add your logic here. 
  }    
}

Private Sub chartControl1_AnnotationRepositoryChanging(ByVal sender As Object, ByVal e As AnnotationRepositoryChangingEventArgs)
    If e.Change = AnnotationRepositoryChange.Text Then
        Dim textEditingArgs As AnnotationTextEditingEventArgs = CType(e, AnnotationTextEditingEventArgs)
        Dim newAnnotationText As String = textEditingArgs.NewText
        'Add your logic here.
    End If
End Sub