oca-ocb-pos/odoo-bringout-oca-ocb-pos_hr/pos_hr/views/pos_order_view.xml

<?xml version="1.0" encoding="utf-8"?>
<odoo>
    <record id="pos_order_form_inherit" model="ir.ui.view">
        <field name="name">pos.order.form.inherit</field>
        <field name="model">pos.order</field>
        <field name="inherit_id" ref="point_of_sale.view_pos_pos_form"/>
        <field name="arch" type="xml">
            <xpath expr="//field[@name='user_id']" position='replace'>
                <field string='Cashier' name="employee_id" readonly="1" attrs="{'invisible': [('employee_id','=',False)]}"/>
                <field string='Cashier' name="user_id" readonly="1" attrs="{'invisible': [('employee_id','!=',False)]}"/>
            </xpath>
        </field>
    </record>

    <record id="pos_order_list_select_inherit" model="ir.ui.view">
        <field name="name">pos.order.list.select.inherit</field>
        <field name="model">pos.order</field>
        <field name="inherit_id" ref="point_of_sale.view_pos_order_filter"/>
        <field name="arch" type="xml">
            <xpath expr="//field[@name='user_id']" position="replace">
                <field name="cashier"/>
            </xpath>
            <xpath expr="//filter[@name='user_id']" position="replace">
                <filter string="Cashier" name="by_cashier" domain="[]" context="{'group_by': 'cashier'}"/>
            </xpath>
        </field>
    </record>

    <record id="view_pos_order_tree_inherit" model="ir.ui.view">
        <field name="name">pos.order.tree.inherit</field>
        <field name="model">pos.order</field>
        <field name="inherit_id" ref="point_of_sale.view_pos_order_tree"/>
        <field name="arch" type="xml">
            <xpath expr="//field[@name='user_id']" position="replace">
                <field name="employee_id" widget="many2one_avatar_employee"/>
            </xpath>
        </field>
    </record>
</odoo>