In the end I opened a case with the Support.
They told me that the service is still sperimental, so not ufficially supported yet, and it has to be used only if requested by Qlik Support.
At this time they weren't able to give me more details about it. Also, QLogs should be the database where this service writes.
There is an article on Qlik Support (that I completely missed) that reports the fact that it is not supported: 000036354 - "Qlik Logging Service" in Qlik Sense June 2017 release.