pos/pos_order_return_traceability/views/pos_templates.xml

<?xml version="1.0" encoding="utf-8"?>
<odoo>

    <template id="assets" inherit_id="point_of_sale.assets">
        <xpath expr="." position="inside">
            <script src="/pos_order_return_traceability/static/src/js/models.js"
                    type="text/javascript"></script>
            <script src="/pos_order_return_traceability/static/src/js/widgets.js"
                    type="text/javascript"></script>
        </xpath>
    </template>

</odoo>