gs.info(getDuplicates('cmdb_ci_service','u_service_id'));

function getDuplicates(tablename,val) {
  var dupRecords = [];
  var gaDupCheck = new GlideAggregate(tablename);
  gaDupCheck.addQuery('active','true');
  gaDupCheck.addAggregate('COUNT',val);
  gaDupCheck.addNotNullQuery(val);
  gaDupCheck.groupBy(val);
  gaDupCheck.addHaving('COUNT', '>', 1);
  gaDupCheck.query();
  while (gaDupCheck.next()) {
      dupRecords.push(gaDupCheck[val].toString());  
  }
  return dupRecords;
}