How will I know that my request (PTO/SB/38) and/or authorization (PTO/SB/39) have been received by the USPTO?

The request and/or authorization will be viewable via PAIR[link] definition - PAIR.

The filing receipt will include one or both of the following texts:

Request to Retrieve - This application either claims priority to one or more applications filed in an intellectual property Office that participates in the Priority Document Exchange (PDX) program or contains a proper Request to Retrieve Electronic Priority Applications(s) (PTO/SB/38 or its equivalent). Consequently, the USPTO will attempt to electronically retrieve these priority documents.

Permission to Access - A proper Authorization to Permit Access to Application by Participating Office (PTO/SB/39 or its equivalent) has been received by the USPTO.

USPTO FAQ - Questions and Answers (31JUL2009)