These are some key log files and config files in OBIEE 11g. These might be frequently accessed for debugging and checking current parameter settings.

bi_server1.log  &  bi_server1-diagnostic.log
(bi_server1.out  &  access.log are also captured in this directory)
[$FMW_HOME]/user_projects/domains/bifoundation_domain/servers/bi_server1/logs

nqserver.log    &    nqquery.log
[$FMW_HOME]/instances/instance1/diagnostics/logs/OracleBIServerComponent/coreapplication_obis1

sawlog.log
[$FMW_HOME]/instances/instance1/diagnostics/logs/OracleBIPresentationServicesComponent/coreapplication_obips1

NQSConfig.INI   &  DBFeatures.INI
[$FMW_HOME]/instances/instance1/config/OracleBIServerComponent/coreapplication_obis1

instanceconfig.xml      &     credentialstore.xml
[$FMW_HOME]/instances/instance1/config/OracleBIPresentationServicesComponent/coreapplication_obips1

config.xml
[$FMW_HOME]/user_projects/domains/bifoundation_domain/config

system-jazn-data.xml
[$FMW_HOME]/user_projects/domains/bifoundation_domain/config/fmwconfig