Hi,
In the delivery note analysis window you can see the connected customer order line there. You can go to customer order (Zoom option is also available and you can go to the CO directly using that) and then you can go to invoice info by using RMB customer order. Hope this information is helpful.
There is no one to one connection between Delivery Note and the Invoice. There cannot be too.
For example, if a Customer Order has 2 parts they might be invoiced with 2 separate invoices but still delivered under one Delivery Note. In this scenario one Delivery Note has 2 Invoices. Invoices are always connected to respective Order Lines, Delivery notes too but not necessary to the same lines.