To Write message in event log by dynamics axapta code x++ you can try following code in job of AOT.
System.Diagnostics.EventLog EventLogObj = new System.Diagnostics.EventLog();
;
EventLogObj.set_Source(‘Dynamics Axapta -Message from Admin’);
EventLogObj.WriteEntry("This is just checking of message in event log form Dynamics ax");
EventLogObj.Close();