How to add click event to a-image in ar-js

try add

<script>
    AFRAME.registerComponent('clickhandler', {
        init: function() {
            this.el.addEventListener('click', () => {
                alert('Clicked!')
            });
    }});
</script>

and add clickhandler attributes to your a-image, like <a-image clickhandler ... >

Source: https://github.com/AR-js-org/AR.js/blob/master/aframe/examples/location-based/click-places/index.html