Resolution:
In the Field Summary section of the FTPClient Javadoc, there is a list of variables that are maintained by the FTPClient.  To access these variables, use the following procedure when coding in ECMAScript:

1.  In the documentation, click on the variable you are interested in.  For this example, use "TRANSACTION_ID".  The documentation will jump to the section of code that describes the variable.

2.  Click on the "Constant Field Values" hyperlink.  You will see the list of variables as well as a string that is referenced by the variable.  In the case of "TRANSACTION_ID", the string is "transactionID".

3.  Use the string in the job.get command to retrieve it's value.  in the case of TRANSACTION_ID, the command would be:

job.get("transactionID");