You can’t load glTF data directly because it’s not georeferenced.

You can paint it as a 3D icon in your own IFeaturePainterIFeaturePainterIFeaturePainter though, using an Icon3D draw command. The map displays the mesh at the location you specify for a point.

Program: Visualizing glTF Data
class Icon3DPainter final : public IFeaturePainter {
public:
  explicit Icon3DPainter(std::string& source) : _source{source} {};

  void configureMetadata(luciad::FeaturePainterMetadata& metadata) const override {
  }

  void paint(const luciad::Feature& feature, const luciad::FeaturePainterContext& /*context*/, luciad::FeatureCanvas& canvas) const override {
    auto geometry = feature.findGeometry();
    if (!geometry) {
      return;
    }

    auto point = std::dynamic_pointer_cast<Point>(geometry);
    if (!point) {
      return;
    }

    canvas.drawIcon3D()
        .position(point)
        .source(_source)
        .orientation(0.0, 0.0, 30.0)
        .scale(5.0, 5.0, 5.0)
        .transparency(true)
        .submit();
  }

private:
  std::string _source;
};
private class Icon3DPainter : IFeaturePainter
{
    private readonly string _source;

    public Icon3DPainter(string source)
    {
        _source = source;
    }

    public void ConfigureMetadata(FeaturePainterMetadata metadata)
    {
    }

    public void Paint(Feature feature, FeaturePainterContext context, FeatureCanvas canvas)
    {
        var point = feature.FindGeometry() as Point;
        if (point == null)
        {
            return;
        }

        canvas.DrawIcon3D()
            .Position(point)
            .Source(_source)
            .Orientation(0.0, 0.0, 30.0)
            .Scale(5.0, 5.0, 5.0)
            .Transparency(true)
            .Submit();
    }
}
class Icon3DPainter(private val source: String) : IFeaturePainter {

    override fun configureMetadata(metadata: FeaturePainterMetadata) {
    }

    override fun paint(
        feature: Feature,
        context: FeaturePainterContext,
        canvas: FeatureCanvas
    ) {
        (feature.findGeometry() as? Point)?.let {
            canvas.drawIcon3D()
                .position(it)
                .source(source)
                .orientation(Azimuth(0.0), Angle(0.0), Angle(30.0))
                .scale(5.0, 5.0, 5.0)
                .transparency(true)
                .submit()
        }
    }
}

For more information about LuciadCPillar’s glTF support, see Which glTF version is supported and what are the limitations?