Many thanks for the code jarry, i got it to work with a few changes and here is the final code. It now works perfectly

function onContextMenu(e,row){
e.preventDefault();
$(this).treegrid('select', row.id);
var tr = $(e.target).closest('tr.datagrid-row');
if (tr.length && tr.parent().length){
var id = tr.attr('node-id');
var field = $(e.target).closest('td[field]').attr('field');
alert(id+":"+field);
}
if (row.norm != '') {
$('#mm').menu('show',{
left: e.pageX,
top: e.pageY
});
} else {
$('#mmShort').menu('show',{
left: e.pageX,
top: e.pageY
});
}
}