public void Create( 
   IndexDescription indexDescription
)

public void CreatingTableWithIndex(SchemaBuilder schemaBuilder)
{
    FieldDescription nameFieldDescription = FieldDescription.CreateStringField("Name", 50);
    FieldDescription addressFieldDescription = FieldDescription.CreateStringField("Address", 200);

    // Creating a feature class, 'Buildings' with two fields
    TableDescription tableDescription = new TableDescription("Buildings", new List<FieldDescription>() { nameFieldDescription, addressFieldDescription });

    // Enqueue DDL operation to create a table
    TableToken tableToken = schemaBuilder.Create(tableDescription);

    // Creating an attribute index named as 'Idx'
    AttributeIndexDescription attributeIndexDescription = new AttributeIndexDescription("Idx", new TableDescription(tableToken),
      new List<string> { nameFieldDescription.Name, addressFieldDescription.Name });

    // Enqueue DDL operation to create an attribute index
    schemaBuilder.Create(attributeIndexDescription);

    // Execute build indexes operation
    bool isBuildSuccess = schemaBuilder.Build();
}

public void AddingIndexes(SchemaBuilder schemaBuilder, FeatureClassDefinition featureClassDefinition)
{
    // Field names to add in the attribute index
    string fieldName = featureClassDefinition.GetFields().First(f => f.AliasName.Contains("Name")).Name;
    string fieldAddress = featureClassDefinition.GetFields().First(f => f.AliasName.Contains("Address")).Name;

    // Creating an attribute index with index name 'Idx' and two participating fields' name
    AttributeIndexDescription attributeIndexDescription = new AttributeIndexDescription("Idx", new TableDescription(featureClassDefinition), new List<string> { fieldName, fieldAddress });

    // Enqueue DDL operation for an attribute index creation 
    schemaBuilder.Create(attributeIndexDescription);

    // Creating the spatial index 
    SpatialIndexDescription spatialIndexDescription = new SpatialIndexDescription(new FeatureClassDescription(featureClassDefinition));

    // Enqueue DDL operation for the spatial index creation
    schemaBuilder.Create(spatialIndexDescription);

    // Execute build indexes operation
    bool isBuildSuccess = schemaBuilder.Build();

    if (!isBuildSuccess)
    {
        IReadOnlyList<string> errors = schemaBuilder.ErrorMessages;
        // Iterate and handle errors 
    }
}

await QueuedTask.Run(() =>
{
  using (var kg = GetKnowledgeGraph())
  {
    if (kg == null)
      return;

    var entity_name = "PhoneCall";

    //indexes are managed on the GDB objects...
    var entity_table_def = kg.GetDefinition<TableDefinition>(entity_name);
    var entity_table_desc = new TableDescription(entity_table_def);


    var entity_table_flds = entity_table_def.GetFields();
    AttributeIndexDescription attr_index1 = null;
    AttributeIndexDescription attr_index2 = null;
    foreach (var fld in entity_table_flds)
    {
      //index the first string field
      if (fld.FieldType == FieldType.String && attr_index1 == null)
      {
        if (fld.Name == "ESRI__ID")//special case
          continue;
        //Index _must_ be ascending for KG
        attr_index1 = new AttributeIndexDescription(
          "Index1", entity_table_desc, new List<string> { fld.Name })
        {
          IsAscending = true
        };
      }
      //index the first numeric field (if there is one)
      if ((fld.FieldType == FieldType.BigInteger ||
           fld.FieldType == FieldType.Integer ||
           fld.FieldType == FieldType.Single ||
           fld.FieldType == FieldType.SmallInteger ||
           fld.FieldType == FieldType.Double) && attr_index2 == null)
      {
        attr_index2 = new AttributeIndexDescription(
          "Index2", entity_table_desc, new List<string> { fld.Name })
        {
          IsAscending = true,
          IsUnique = true //optional - unique if all values are to be unique in the index
        };
      }
      if (attr_index1 != null && attr_index2 != null) break;
    }

    if (attr_index1 == null && attr_index2 == null)
      return; //nothing to index

    //Run the schema builder
    try
    {
      SchemaBuilder sb = new(kg);
      if (attr_index1 != null)
        sb.Create(attr_index1);
      if (attr_index2 != null)
        sb.Create(attr_index2);
      if (!kg.ApplySchemaEdits(sb))
      {
        var err_msg = string.Join(",", sb.ErrorMessages.ToArray());
        System.Diagnostics.Debug.WriteLine($"Create index error: {err_msg}");
      }
    }
    catch (Exception ex)
    {
      System.Diagnostics.Debug.WriteLine(ex.ToString());
    }
  }
});