ok it works with this below, could you please now have a look at my second question please ? thanks
function my_acf_admin_head()
{
?>
<script type="text/javascript">
jQuery(function($){
$('select').on('change', function() {alert( this.value );})
});
</script>
<?php
}
add_action('acf/input/admin_head', 'my_acf_admin_head');