public class ReportPageHeader : ReportSectionElement, ArcGIS.Desktop.Mapping.IElement, ArcGIS.Desktop.Mapping.IElementContainer, System.ComponentModel.INotifyPropertyChanged, System.IComparable, System.IDisposable, System.IEquatable<Element>  

{
  //Get the "ReportSection element"
  //ReportSectionElement contains the ReportHeader, ReportPageHeader, ReportDetails. ReportPageFooter, ReportFooter sections.
  var mainReportSection = report.Elements.OfType<ReportSection>().FirstOrDefault();

  //Get the ReportHeader
  var reportHeader = mainReportSection?.Elements.OfType<ReportHeader>().FirstOrDefault();

  //Get the ReportHeader
  var reportPageHeader = mainReportSection?.Elements.OfType<ReportPageHeader>().FirstOrDefault();

  //Get the "ReportDetails" within the ReportSectionElement. ReportDetails is where "fields" are.
  var reportDetailsSection = mainReportSection?.Elements.OfType<ReportDetails>().FirstOrDefault();

  //Get the ReportPageFooter
  var reportPageFooter = mainReportSection?.Elements.OfType<ReportPageFooter>().FirstOrDefault();

  //Get the ReportFooter
  var reportFooter = mainReportSection?.Elements.OfType<ReportFooter>().FirstOrDefault();
}