public Task ActivateToolAsync( 
   string damlID
)

{
  await QueuedTask.Run(() =>
  {
    // DAML ID of the tool to activate - for example "esri_editing_SketchTwoPointLineTool" Pro Tool or a custom tool
    string _editToolname = "esri_editing_SketchTwoPointLineTool";

    // Get all templates for the layer
    var templates = featureLayer.GetTemplates();
    if (templates.Count == 0)
      return;
    // Get the first template - alternatively get a specific template
    var template = templates.First();

    // Confirm the tool is available in the template
    if (template.ToolIDs.FirstOrDefault(_editToolname) == null)
      return;

    // Activate the tool
    template.ActivateToolAsync(_editToolname);
  });
}

// Subscribes to the active template changed event and handles changes to the editing template.
ArcGIS.Desktop.Editing.Events.ActiveTemplateChangedEvent.Subscribe(async activeTemplateChangedEventArgs
  =>
{
  // return if incoming template is null
  if (activeTemplateChangedEventArgs.IncomingTemplate == null)
    return;

  // Activate two-point line tool for Freeway template in the Layers map
  if (activeTemplateChangedEventArgs.IncomingTemplate.Name == "Freeway" && activeTemplateChangedEventArgs.IncomingMapView.Map.Name == "Layers")
    await activeTemplateChangedEventArgs.IncomingTemplate.ActivateToolAsync("esri_editing_SketchTwoPointLineTool");
});