Hi,

If you are looking to display/get the no of the stock-able product in the sale order, you can add a compute field in the sale order model and compute the count into it.

stock_product_count = fields.Integer(string='Count', compute='get_pro_count')

@api.multi
def get_pro_count(self):
    for rec in self:
        count = 0
        for line in rec.order_line:
            if line.product_id.type == 'product':
                count += 1
        rec.stock_product_count = count

Thanks