public Report CreateReport( 
   string name,
   ReportCustomTemplateDefinition templateDataDef
)

//Note: Call within QueuedTask.Run()
//The fields in the datasource used for the report
//This uses a US Cities dataset
var listFields = new List<CIMReportField> {
          //Grouping should be the first field
          new CIMReportField{Name = "STATE_NAME", FieldOrder = 0, Group = true, SortInfo = FieldSortInfo.Desc}, //Group cities using STATES
          new CIMReportField{Name = "CITY_NAME", FieldOrder = 1},
          new CIMReportField{Name = "POP1990", FieldOrder = 2, },
      };
//Definition query to use for the data source
var defQuery = "STATE_NAME LIKE 'C%'";
//Define the Datasource
var reportDataSource = new ReportDataSource(featureLayer, defQuery, listFields);
//The CIMPage defintion - page size, units, etc
var cimReportPage = new CIMPage
{
  Height = 11,
  StretchElements = false,
  Width = 6.5,
  ShowRulers = true,
  ShowGuides = true,
  Margin = new CIMMargin { Bottom = 1, Left = 1, Right = 1, Top = 1 },
  Units = LinearUnit.Inches
};

//Report template
var reportTemplates = await ReportTemplateManager.GetTemplatesAsync();
var reportTemplate = reportTemplates.Where(r => r.Name == "Attribute List with Grouping").First();

//Report Styling
var reportStyles = await ReportStylingManager.GetStylingsAsync();
var reportStyle = reportStyles.Where(s => s == "Cool Tones").First();

//Field Statistics
var fieldStatisticsList = new List<ReportFieldStatistic> {
          new ReportFieldStatistic{ Field = "POP1990", Statistic = FieldStatisticsFlag.Sum}
          //Note: NoStatistics option for FieldStatisticsFlag is not supported.
      };
var report = ReportFactory.Instance.CreateReport("USAReport", reportDataSource, cimReportPage, fieldStatisticsList, reportTemplate, reportStyle);

//Note: Run within QueuedTask.Run()
await QueuedTask.Run(() =>
{          
  // get the first map in the project
  MapProjectItem item = Project.Current.GetItems<MapProjectItem>().FirstOrDefault(n => n.Name == "Cities");
  if (item == null)
    return;

  Map map = item.GetMap();
  if (map == null)
    return;

  Layer cityLayer = map.FindLayers("U.S. Cities")[0];
  if (cityLayer == null)
    return;

  // load template information
  var templatePath = System.IO.Path.Combine($@"{Project.Current.HomeFolderPath}\TemplateSimpleReportWithTokens.rptt");
  ReportCustomTemplateDefinition templateDef = ReportTemplateManager.GetCustomTemplateDefinition(templatePath);
  if (templateDef == null || templateDef.ReportTemplateDataSourceItems?.Count() < 1)
    return;

  // get template info of first data source (parent) and set its data source
  ReportCustomTemplateDataSourceInfo parentDataSourceInfo = templateDef.ReportTemplateDataSourceItems.ElementAt(0);

  parentDataSourceInfo.SetReportDataSource(cityLayer);

  TemplateTokenFieldInfoValues templateTokenFieldInfoValues = parentDataSourceInfo.TokenInfoValues;

  parentDataSourceInfo.DefinitionQuery = "STATE_NAME = 'Massachusetts'";
  templateTokenFieldInfoValues["[text-field-value-0]"] = "CITY_NAME";
  templateTokenFieldInfoValues["[text-field-name-0]"] = "City";
  templateTokenFieldInfoValues["[numeric-field-value-0]"] = "POP1990";
  templateTokenFieldInfoValues["[numeric-field-name-0]"] = "Population";

  if (templateDef.CanCreateReport())
  {
    // create the report
    report = ReportFactory.Instance.CreateReport("RelateSiblingsFromCode", templateDef);
  }
});
//UI thread
if (report != null)
{
  //open report
  await FrameworkApplication.Panes.CreateReportPaneAsync(report);
}