public Subtype DestinationSubtype {get;}

{
  static void GetTopologyRules()
  {
    using (Geodatabase geodatabase = new Geodatabase(new FileGeodatabaseConnectionPath(new Uri(@"C:\TestData\GrandTeton.gdb"))))
    using (ArcGIS.Core.Data.Topology.Topology topology = geodatabase.OpenDataset<ArcGIS.Core.Data.Topology.Topology>("Backcountry_Topology"))
    {
      using (TopologyDefinition topologyDefinition = topology.GetDefinition())
      {
        IReadOnlyList<TopologyRule> rules = topologyDefinition.GetRules();

        Console.WriteLine($"There are {rules.Count} topology rules defined for the topology:");
        Console.WriteLine("ID \t Origin Class \t Origin Subtype \t Destination Class \t Destination Subtype \t Rule Type");

        foreach (TopologyRule rule in rules)
        {
          Console.Write($"{rule.ID}");
          Console.Write(!String.IsNullOrEmpty(rule.OriginClass) ? $"\t{rule.OriginClass}" : "\t\"\"");
          Console.Write(rule.OriginSubtype != null ? $"\t{rule.OriginSubtype.GetName()}" : "\t\"\"");
          Console.Write(!String.IsNullOrEmpty(rule.DestinationClass) ? $"\t{rule.DestinationClass}" : "\t\"\"");
          Console.Write(rule.DestinationSubtype != null ? $"\t{rule.DestinationSubtype.GetName()}" : "\t\"\"");
          Console.Write($"\t{rule.RuleType}");
          Console.WriteLine();
        }
      }
    }
  }
}