How to catch click events on a link in order to fire a pixel

You should be able to catch click events with jquery via a customization. Put this in the </head> section:

<script type="text/discourse-plugin" version="0.2">
    Discourse.PageTracker.current().on('change', function () {
        $(".topic-list-item .title").on("click", function(){
            console.log("xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx");
        })
    })
</script>

This will log the string of x`s every time you click on the title of a topic in a list of topics. You could alter this to do whatever you please for every link on the site.