Re: How to connect to Qlik Sense repository database to build a Qlik app to analyse log files, etc?
As @LeviTurner and @gandalfgray pointed out, log information is accessible in the QLogs database in postgres, alongside the Qlik Sense Repository (QSR) database.
You should already have a "QLogs" data connection available to you that might require updating to add proper userId/password but which, in theory, should work out of the box.
Consider using the Log Monitor sense app which is included in Qlik Sense Enterprise installations and can be found with other Monitor Apps in c:\programdata\qlik\sense\repository\defaultApps. You might find that someone has already done some of your work for you already 🙂