Hi Caroline,
I am assuming the question direction is "Column". Please follow below steps:
1. Click on the column option you need to add "%" sign, then edit
2. In cell input labels, write "%" and change the position of the label to "Right" of the input.
You can also directly copy below script in the footer of the question and you can then skip doing above steps:
<script>
$(document).ready(function(){
$(".numeric_input,.total").after(" %");
});
</script>
Regards,
Rahul Mittal