In the UI, you can get a list of processed items linked to a given publish transaction. For instance if you publish a Structure Group, the publishing queue will show the SG. Double click on it and in the processed items tab you can see the full list of pages that were published within that transaction.
How do I get that list through the API? I've been looking deep into the PublishTransactionData object, and can't seem to find any information there about the published/processed items, so it's likely something coming from a different list. There is an Items array in PublishTransactionData, but that seems to only include the item that was originally sent to be published (the structure group in my example above).