You can Subscribe to listen for the ActiveTemplateChangedEvent and specify a delegate that will be executed upon receiving the event. To stop listening, you can Unsubscribe.
ArcGIS.Desktop.Editing.Events.ActiveTemplateChangedEvent.Subscribe(OnActiveTemplateChanged);
asyncvoid 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");
}