Hi,

First of all, there should be a link established between the models sale.order and mrp.production.

To store the value of the sale order in the mrp.production, inherit and add a many2one field of the sale order in it.

class MrpProduction(models.Model):
    _inherit = 'mrp.production'

    sale_order_id = fields.Many2one('sale.order', string='Sale Order')

    partner_id = fields.Many2one('res.partner', related='sale_order_id.partner_id', string="Cusromer")

Also in the above code, we have added a related field of the model res.partner to store the value of the customer in the sale order inside the mrp.production. As it related field it will take the value from the sale.order model.

Then you can inherit the procurement.order model and super the function _prepare_mo_vals to pass the sale order id to the new field added in the mrp.production.

@api.model
def _prepare_mo_vals(self, bom):
    vals = super(ProcurementOrder, self)._prepare_mo_vals(bom)
            if self.group_id:
                    sales = self.env['sale.order'].search([('procurement_group_id', '=', self.group_id.id)])
                    if len(sales) > 1:
                            raise exceptions.ValidationError(_('More than 1 sale order found for this group'))
                    vals['sale_order_id'] = sales.id
    return vals

Now you can inherit the corresponding views and add the newly added fields in the views so that it can be seen in the UI.

For adding the new fields to the existing view, you can check this blog: Add Custom Fields to Existing Views

The code for establishing the connection between sale order and mrp production is taken from this OCA Module: Sale MRP Link

Thanks