Hi,

You can add the customer name to POS ticket by using this code,

<div style="width: 55%; float: left; padding: 20px 0px;">
    <t t-if="order.get_client()">
        Customer: <t t-esc="order.get_client().name"/><br />
     </t>
     Cashier: <t t-esc="widget.pos.cashier ? widget.pos.cashier.name : widget.pos.user.name"/><br />
     <t t-if="widget.pos.company.phone">
        Phone: <t t-esc="widget.pos.company.phone || ''"/><br />
     </t>
     <t t-esc="order.name"/>
     <t t-esc="moment().format('L LT')"/>
</div>

Already there is a community module for this, please check out this app, https://www.odoo.com/apps/modules/11.0/pos_ticket/

Thanks