public KnowledgeGraph GetDatastore()

{
  //var kgLayer = MapView.Active.Map.GetLayersAsFlattenedList()
  //			.OfType<KnowledgeGraphLayer>().FirstOrDefault();

  await QueuedTask.Run(() =>
  {
    // use the layer directly
    KnowledgeGraph datastore = kgLayer.GetDatastore();

    // or you can use any of the sub items since
    //KnowledgeGraphLayer is a composite layer - get the first 
    // child feature layer or standalone table
    var featlayer = kgLayer?.GetLayersAsFlattenedList()?
                    .OfType<FeatureLayer>()?.FirstOrDefault();
    KnowledgeGraph kg = null;
    if (featlayer != null)
    {
      using (var fc = featlayer.GetFeatureClass())
        kg = fc.GetDatastore() as KnowledgeGraph;
      //TODO use KnowledgeGraph
    }
    else
    {
      //try standalone table
      var stbl = kgLayer?.GetStandaloneTablesAsFlattenedList()?
                      .FirstOrDefault();
      if (stbl != null)
      {
        using (var tbl = stbl.GetTable())
          kg = tbl.GetDatastore() as KnowledgeGraph;
        //TODO use KnowledgeGraph
      }
    }
  });
}

{
  var kg_layer = MapView.Active.Map.GetLayersAsFlattenedList()
                  .OfType<KnowledgeGraphLayer>().FirstOrDefault();
  if (kg_layer == null)
    return;

  await QueuedTask.Run(() =>
  {
    // get the datastore
    var kg = kg_layer.GetDatastore();

    // now submit a search or a query
    // kg.SubmitSearch
    // kg.SubmitQuery
  });
}