The local files will generate automatically once logging is added to policies for all but very high end devices. These default to stream instead of local mode but can be shifted to local file logging by configuration if that is preferred.
Reading this thread again, I probably missed the main point for the specific question. The question was how to I read these log files outside the SRX. But the main point seems to be wanting to centrally log and keep information long term.
The SRX does support syslog as the format to ship logs directly off the device to a central repository like a log collector or SIEM. You simply configure that target and details in syslog and the events will be directly sent there as well for long term storage and analysis.