public T FindClosestElement<T>( 
   MapPoint queryPoint,
   double searchRadius
)
where T: TopologyElement

public void FindClosestElement()
{
  using (Geodatabase geodatabase = new Geodatabase(new FileGeodatabaseConnectionPath(new Uri(@"C:\TestData\GrandTeton.gdb"))))
  using (Topology topology = geodatabase.OpenDataset<Topology>("Backcountry_Topology"))
  {
    // Build a topology graph using the extent of the topology dataset.

    topology.BuildGraph(topology.GetExtent(), (topologyGraph) =>
    {
      MapPoint queryPointViaCampsites12 = null;

      using (Feature campsites12 = GetFeature(geodatabase, "Campsites", 12))
      {
        queryPointViaCampsites12 = campsites12.GetShape() as MapPoint;
      }

      double searchRadius = 1.0;

      TopologyElement topologyElementViaCampsites12 = 
          topologyGraph.FindClosestElement<TopologyElement>(
                    queryPointViaCampsites12, searchRadius);

      System.Diagnostics.Debug.Assert(
        topologyElementViaCampsites12 != null, "There should be a topology element corresponding to 'queryPointViaCampsites12' within the 'searchRadius' units.");

      IReadOnlyList<FeatureInfo> parentFeatures = topologyElementViaCampsites12.GetParentFeatures();

      Console.WriteLine("The parent features that spawn 'topologyElementViaCampsites12' are:");
      foreach (FeatureInfo parentFeature in parentFeatures)
      {
        Console.WriteLine($"\t{parentFeature.FeatureClassName}; OID: {parentFeature.ObjectID}");
      }

      TopologyNode topologyNodeViaCampsites12 = topologyGraph.FindClosestElement<TopologyNode>(queryPointViaCampsites12, searchRadius);

      if (topologyNodeViaCampsites12 != null)
      {
        // There exists a TopologyNode nearest to the query point within searchRadius units.
      }

      TopologyEdge topologyEdgeViaCampsites12 = topologyGraph.FindClosestElement<TopologyEdge>(queryPointViaCampsites12, searchRadius);

      if (topologyEdgeViaCampsites12 != null)
      {
        // There exists a TopologyEdge nearest to the query point within searchRadius units.
      }
    });
  }
}