Chrome DevTools Console Hack to list all Data Attributes in table view. Credits to: https://www.thyngster.com/tip-quickly-debugqa-data-attributes/ For GTM I assume. [updated June 28, 2017]

Data-Attributes-Console-Hack.js

(function() {
    
    var elements = [].slice.call(document.querySelectorAll('*')).filter(function(el) {
        if (typeof (el.dataset) != "undefined")
            return Object.keys(el.dataset).length != 0;
    });
    
    var data = [];
    var i = elements.length;
    
    while (i--) {
        var el = JSON.parse(JSON.stringify(elements[i].dataset));
        data.push(el);
        el["_element_type"] = elements[i].nodeName;
    }
    console.table(data);
})();