TZ00 is the ThermalZone sensor on the CPU which monitors the CPU temperature.
Different makes and models of CPU have different safe working temperatures, so 68C. on it's own doesn't mean much. You would need to know the make/model of CPU if you want to find out if 68C. is too high.
When you know the CPU details, Googling it should bring up the safe temperature limit information if you type in a suitable search criteria.