You can modify the QWEB report template, ideally inheriting and overriding the report provided by Odoo.

Take a look at the report called report_saleorder_document

To show the Currency after where Payment Terms would be shown, add this after the Payment Terms div:

 <div t-if="o.pricelist_id.currency_id" class="col-xs-3">
   <strong>Currency:</strong>
   <p t-field="o.pricelist_id.currency_id.name"/>
 </div>