If you add the following code to the XPages CSJS onClientLoad event then it will add an id attribute to each of the page link nodes and then set the tooltip for each of those nodes.
var nl = dojo.query("div header ul li a");
var i = 1;
dojo.forEach(nl, function(selectedItem) {
dojo.attr(selectedItem, {
id: "selected"+ i
})
i+=1;
}); // end forEach
new dijit.Tooltip({
connectId: "selected1",
label: "This is the tooltip for node 1"
});
new dijit.Tooltip({
connectId: "selected2",
label: "This is the tooltip for node 2"
});
new dijit.Tooltip({
connectId: "selected3",
label: "This is the tooltip for node 3"
});