Hi,

sale_id = self.procurement_group_id.mrp_production_ids.move_dest_ids.group_id.sale_id.id

by this you can get the sale order related to the particular manufacturing order, and from that by calling sale_id.order_line , we get all the order lines of the current sale order( sale_id). By looping ( for line in sale_id.order_line), we get each order and by applying certain condition ( to get the particular order line) and call line.field_name inside the loop for accessing the field value for the current order line.

Regards

Have you seen https://www.odoo.com/forum/help-1/pull-information-from-a-sales-order-the-description-on-the-line-to-the-related-mto-production-order-171624