Hello Iain,
You can see which Jobs have had an Invoice Sent/Printed to the Customer from the Invoicing Tab in your account.
Most teams find the best workflow is to ensure this is done before Approving Jobs.
If you are looking for more of a report of these, you should be able to get that by performing an export of your Jobs from Reporting. More that this, our DDD Reporting services could easily provide such a report (and much more) as well in a more consistent way. However I am at a lose as to what benefit having such a report external of the data presented from the Invoicing Tab would provide.