DeprecationReportBody.lineNumber

let options = {
  types: ['deprecation'],
  buffered: true
}

let observer = new ReportingObserver(function(reports, observer) {
  let firstReport = reports[0];
  console.log(firstReport.type); // deprecation
  console.log(firstReport.body.sourceFile); // the source file
  console.log(firstReport.body.lineNumber); // the line in that file
}, options);