How to get the element clicked (for the whole document)?

You need to use the event.target which is the element which originally triggered the event. The this in your example code refers to document.

In jQuery, that’s…

$(document).click(function(event) {
    var text = $(event.target).text();
});

Without jQuery…

document.addEventListener('click', function(e) {
    e = e || window.event;
    var target = e.target || e.srcElement,
        text = target.textContent || target.innerText;   
}, false);

Also, ensure if you need to support < IE9 that you use attachEvent() instead of addEventListener().