@abhishekroy168, refer to one of previous answers which highlights this issue of including setTimeOut() for JavaScript to work. https://answers.splunk.com/answers/614788/splunk-dashboard-examples-table-row-highlighting-b.html
I think this issue is also on similar lines. If you have tried a code like below please confirm and accept the answers, otherwise requesting you to provide and accept your own answer to help the others.
$("#element1").on("mouseover", " g.highcharts-series-group > g.highcharts-series-hover", function(){
setTimeout(function(){
var title = $("table.highcharts-tooltip > tbody > tr:nth-child(1) > td:nth-child(2)").text();
alert(title);
}, 10);
});
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