Another example for displaying GEONExT
From JSXGraph Wiki
<div id="box" class="jxgbox" style="width:500px; height:500px;"></div>
<script type="text/javascript">
var brd = JXG.JSXGraph.loadBoardFromFile('box', 'http://jsxgraph.uni-bayreuth.de/geonext/Unendlich.gxt', 'Geonext');
</script>