I've just had a quick look at this -
The "Job Summary" is actually printed using windows, so you can Print to Pdf and save digitally on your system in a matter of seconds but you can't extract the data from this.
I would also note that in the past I've had issues where the job log gets so big it needs to be cleared as was causing issues so be aware of this.
You can automate it in Fiery to export as CSV -
Manage the Job Log
You can also export manually as tabbed pdf which may be easier to review.
As mentioned once you have "Sheets" and "Total Clicks" you can clearly see if the job was double sided at a glance for most jobs.
Your automated auditing process should be able to use this info to create an additional field of Duplex.
As I previously suggested the log is a record of the PRECISE job output from the machine and duplex isn't a simple Yes or No Answer for the machine. Odd page count, blank sheets, mixed media etc will not return a Yes or No answer. I agree it could possibly log "Total Number of Duplexed Pages" & "Total Number of Simplex Pages" but this in itself could create more questions than answers when using it to quality control a printed job.
POSSIBLE SOLUTION -
After I wrote above I realised that the problem really comes down to that the JOB LOG is output data where as the JOB SUMMARY is input data which contains the duplex instruction.
So in CWS you can go to your COMPLETED jobs tab and add the field Duplex (displays values - Off, Top-top, Top-bottom).
Unfortunately it's a manual process but you can
File - Export Current View - and save the Completed Job Data as comma seperated txt file.