Hi,

You may try the following code in your sale order report, to get the account details of customer:

Account number:
 <t t-if="o.partner_id.parent_id.bank_ids">
    <span t-field="o.partner_id.parent_id.bank_ids.acc_number"/> 
 </t>
 <t t-if="o.partner_id.bank_ids">
    <span t-field="o.partner_id.bank_ids.acc_number"/> 
 </t>

But this works only if it contains only one bank account linked. If multiple bank accounts, you need to iterate in bank_ids using t-foreach like in the case  o.order_line.

If having multiple accounts, you may try the following code:

       <h3> Account Details </h3>
	<table>
	       <thead>
	            <tr>
	                <th style="width:20%;"> Bank </th>
	                <th style="width:20%;"> Account No. </th>
	                                              
	            </tr>
	       </thead>
	       <tbody>
		        <t t-if="o.partner_id.parent_id.bank_ids">
		                <tr t-foreach="o.partner_id.parent_id.bank_ids" t-as="b">
		                        <td><span t-field="b.bank_name"/></td>
		                        <td><span t-field="b.acc_number"/></td>
		                </tr>
			</t>
			<t t-if="o.partner_id.bank_ids">
				<tr t-foreach="o.partner_id.bank_ids" t-as="b">
		                    <td><span t-field="b.bank_name"/></td>
		                    <td><span t-field="b.acc_number"/></td>
		                </tr>
			</t>
	        </tbody>
	</table>

Hope this helps.