Looking through the issues for jqplot, it would seem that there have been a few requests for this functionality, but it has not yet been implemented.
Based on this question How to display tooltips on jqplot pie chart, you could wire up the jqplotDataHighlight
and jqplotDataUnhighlight
events:
$("#chartId").bind('jqplotDataHighlight', function(ev, seriesIndex, pointIndex, data) {
});
$("#chartId").bind('jqplotDataUnhighlight', function(ev, seriesIndex, pointIndex, data) {
});
There is a good example of using this technique to create custom tooltips here. Although it is dealing with bubble charts, it should point you in the right direction.
You could also try out the jqplot-highlighter plugin, which allows tooltips for pie charts.