You can access the trace files in the following ways
1.Log in to the portal using the following url http://<hostname>:<portno>/nwa
Navigate to NWA -> Monitoring-> Logs and Traces -> from the dropdown select default trace.
2. If we have the O.S level credentials then all trace information is written to file defaultTrace.trc in directory \usr\sap\<SID>\JC<InstNo>\j2ee\cluster\server<n>\log on the J2EE Server.
Additional Information about Default Trace can be found in below link