Which logs to be validated if automation jobs got failed in agent side?

Following log file needs to be checked-

C:\Program Files (x86)\SapphireIMSAgent\Log\SapphireIMSAgent.log

Along with current log file (latest) file you may need to check backup logs available with extensions log.1, log.2, log.3, log.4, log.5 as failure log messages might be overwritten with some other logs in current one when log file exceeds certain size.