public sealed class SurfaceConstraint 

{
  var constraintCount = lasDataset.GetSurfaceConstraintCount();
  IReadOnlyList<ArcGIS.Core.Data.Analyst3D.SurfaceConstraint> constraints = lasDataset.GetSurfaceConstraints();
  foreach (var constraint in constraints)
  {
    var dsName = constraint.DataSourceName;
    var wksPath = constraint.WorkspacePath;
    var heightField = constraint.HeightField;
    var surfaceType = constraint.SurfaceType;
  }
}

{
  // Note: Needs QueuedTask to run
  {
    var activeSurfaceConstraints = lasDatasetLayer.GetActiveSurfaceConstraints();

    // clear all surface constraints (i.e. none are active)
    lasDatasetLayer.SetActiveSurfaceConstraints(null);

    // set all surface constraints active
    using (lasDataset = lasDatasetLayer.GetLasDataset())
    {
      var surfaceConstraints = lasDataset.GetSurfaceConstraints();
      var names = surfaceConstraints.Select(sc => sc.DataSourceName).ToList();
      lasDatasetLayer.SetActiveSurfaceConstraints(names);
    }
  }
}