Hi,

I think you are trying pass the sale.order date to another model sale.order.line to achieve this use related:

from odoo import models, fields

class SaleOrderLine(models.Model):
    _inherit = 'sale.order.line'

order_date = fields.Datetime(related='order_id.date_order', string='Order Date')

In the XML View:

<record model="ir.ui.view" id="sale_order_line_view_inherit">
<field name="name">sale.order.line.view.inherit</field>
<field name="model">sale.order.line</field>
<field name="inherit_id" ref="sale.view_order_line_tree"/>

    <field name="arch" type="xml">
<xpath expr="field[@name='price_unit']" position="after">
            <field name="order_date"/> </xpath>
    </field>
</record>

Hope it helps