public SpatialQueryFilter()

public async Task SearchingAFeatureClass()
{
    await ArcGIS.Desktop.Framework.Threading.Tasks.QueuedTask.Run(() =>
    {
        using (Geodatabase geodatabase = new Geodatabase(new DatabaseConnectionFile(new Uri("path\\to\\sde\\file\\sdefile.sde"))))
        using (FeatureClass schoolBoundaryFeatureClass = geodatabase.OpenDataset<FeatureClass>("LocalGovernment.GDB.SchoolBoundary"))
        {
            // Using a spatial query filter to find all features which have a certain district name and lying within a given Polygon.
            SpatialQueryFilter spatialQueryFilter = new SpatialQueryFilter
            {
                WhereClause = "DISTRCTNAME = 'Indian Prairie School District 204'",
                FilterGeometry = new PolygonBuilderEx(new List<Coordinate2D>
          {
      new Coordinate2D(1021880, 1867396),
      new Coordinate2D(1028223, 1870705),
      new Coordinate2D(1031165, 1866844),
      new Coordinate2D(1025373, 1860501),
      new Coordinate2D(1021788, 1863810)
          }).ToGeometry(),

                SpatialRelationship = SpatialRelationship.Within
            };

            using (RowCursor indianPrairieCursor = schoolBoundaryFeatureClass.Search(spatialQueryFilter, false))
            {
                while (indianPrairieCursor.MoveNext())
                {
                    using (Feature feature = (Feature)indianPrairieCursor.Current)
                    {
                        // Process the feature. For example...
                        Console.WriteLine(feature.GetObjectID());
                    }
                }
            }
        }
    });
}