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

You can use it as a 3D icon style, though, when you visualize a point. The map then shows the glTF 3D mesh at the location specified by the point: 

const painter = new FeaturePainter();
painter.paintBody = function(geoCanvas, feature, shape, layer, map, paintState) {
  const icon3DStyle = {
    meshUrl: "car.gltf"
  };
  geoCanvas.drawIcon3D(shape, icon3DStyle);
}

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