How to get data attribute in Custom JavaScript variable?

[ulli_s (ulli)]

You can use the dataLayer to access the clicked element:

function () {
 if (TagManager.dataLayer.get('mtm.clickElement')) {
     return TagManager.dataLayer.get('mtm.clickElement').getAttribute('data-foo');
 } else { 
     return '';
 }
}

Worked for me