public Task ActivateToolAsync( 
   string damlID
)

// DAML ID of the tool to activate - for example "esri_editing_SketchTwoPointLineTool" Pro Tool or a custom tool
string _editToolname = "esri_editing_SketchTwoPointLineTool";

// 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);

ArcGIS.Desktop.Editing.Events.ActiveTemplateChangedEvent.Subscribe(OnActiveTemplateChanged);

async void OnActiveTemplateChanged(ArcGIS.Desktop.Editing.Events.ActiveTemplateChangedEventArgs args)
{
  // return if incoming template is null
  if (args.IncomingTemplate == null)
    return;

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