public IReadOnlyList<SurfaceConstraint> GetActiveSurfaceConstraints()

var activeSurfaceConstraints = lasDatasetLayer.GetActiveSurfaceConstraints();

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

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