Hello Hibou,

I wrote this script within a scheduled action and seems to work:

internal_reference = "DESK0004"

sale_order_lines_quantity = sum(

  env["sale.order.line"].search

  (

    ["&", ("product_id.default_code", "=", internal_reference), ("order_id.state", "=", "draft")]

  ).mapped("product_uom_qty")

)

raise Warning(sale_order_lines_quantity)

The idea behind it is that you are searching for all sales orders lines where the order_id (related sales order) is in the draft stage (quotation). You then search on the product_id.default_code to check that the sales order line is the product you are looking for. You then map by the quantity and get the sum. 

I hope this helps.

Thanks,