The report.on should work based on my test. Ensure that var report is in the correct context.
<html><script src="https://microsoft.github.io/PowerBI-JavaScript/demo/node_modules/jquery/dist/jquery.js"></script><script src="https://microsoft.github.io/PowerBI-JavaScript/demo/node_modules/powerbi-client/dist/powerbi.js"></script><script type="text/javascript">
window.onload = function () {
var embedConfiguration = {
type: 'report',
accessToken: 'Token',
id: 'reportid',
embedUrl: 'https://app.powerbi.com/reportEmbed?reportId=d99e763f-xxxx'
};
var $reportContainer = $('#reportContainer');
var report = powerbi.embed($reportContainer.get(0), embedConfiguration);
report.on('loaded', function() {
console.log('report.on - loaded');
});
}
</script><div id="reportContainer" powerbi-settings-nav-content-pane-enabled="true" powerbi-settings-filter-pane-enabled="true"></div></html>
