Edit in JSFiddle

var viewer = null

function initMap() {
  viewer = iv.getViewer();

  var tbx = viewer.getMap().getControlsByClass('Geoportal.Control.ToolBox')[0];
  var panel = new Geoportal.Control.Panel({
    div: OpenLayers.Util.getElement(tbx.id + '_search')
  });

  var gazetteer = new Geoportal.Control.LocationUtilityService.GeoNames(
    new Geoportal.Layer.OpenLS.Core.LocationUtilityService(
      'PositionOfInterest:OPENLS;Geocode', //layer name
      {
        maximumResponses: 100
      }
    ), {
      //Ajout de l'autocomplétion
      autoCompleteOptions: {}
    }
  );

  panel.addControls([gazetteer]);
  viewer.getMap().addControls([panel]);

}

iv = Geoportal.load(
  'viewerDiv', ['jhyvi0fgmnuxvfv0zjzorvdn'], { // Positionnement par coordonnées
    lon: 2.294,
    lat: 48.858
  },
  15, {
    onView: initMap,
    layers: ['ORTHOIMAGERY.ORTHOPHOTOS'],
    viewerClass: Geoportal.Viewer.Default
  }
);
#viewerDiv {
  width: 100%;
  height: 400px;
}

#info {
  padding: 5px;
  width: 100%;
  height: 20px;
  font-family: "monospace";
  font-size: 10px;
}
<div id="viewerDiv"></div>
<div id="info"></div>

External resources loaded into this fiddle: