public IReadOnlyList<T> GetDefinitions<T>()
where T: Definition

public async Task ObtainingDefinitionsFromGeodatabase()
{
    await ArcGIS.Desktop.Framework.Threading.Tasks.QueuedTask.Run(() =>
    {
        using (Geodatabase geodatabase = new Geodatabase(new DatabaseConnectionFile(new Uri("path\\to\\sde\\file\\sdefile.sde"))))
        {
            IReadOnlyList<FeatureClassDefinition> enterpriseDefinitions = geodatabase.GetDefinitions<FeatureClassDefinition>();
            IEnumerable<Definition> featureClassesHavingGlobalID = enterpriseDefinitions.Where(definition => definition.HasGlobalID());

            IReadOnlyList<FeatureDatasetDefinition> featureDatasetDefinitions = geodatabase.GetDefinitions<FeatureDatasetDefinition>();
            bool electionRelatedFeatureDatasets = featureDatasetDefinitions.Any(definition => definition.GetName().Contains("Election"));

            IReadOnlyList<AttributedRelationshipClassDefinition> attributedRelationshipClassDefinitions = geodatabase.GetDefinitions<AttributedRelationshipClassDefinition>();

            IReadOnlyList<RelationshipClassDefinition> relationshipClassDefinitions = geodatabase.GetDefinitions<RelationshipClassDefinition>();
        }
    });
}

public async Task GetFeatureClassesInRelationshipClassAsync()
{
    await ArcGIS.Desktop.Framework.Threading.Tasks.QueuedTask.Run(() =>
    {
        using (Geodatabase geodatabase = new Geodatabase(new FileGeodatabaseConnectionPath(new Uri(@"C:\Data\LocalGovernment.gdb"))))
        {
            IReadOnlyList<RelationshipClassDefinition> relationshipClassDefinitions = geodatabase.GetDefinitions<RelationshipClassDefinition>();

            foreach (RelationshipClassDefinition relationshipClassDefinition in relationshipClassDefinitions)
            {
                IReadOnlyList<Definition> definitions = geodatabase.GetRelatedDefinitions(relationshipClassDefinition, DefinitionRelationshipType.DatasetsRelatedThrough);

                foreach (Definition definition in definitions)
                {
                    System.Diagnostics.Debug.WriteLine($"Feature class in the RelationshipClass is:{definition.GetName()}");
                }
            }
        }
    });
}