Got the log4j.properties of the application.
It is located in {RTC_install_folder}/server/conf/<application>

Edit the ETL's section, it should look like snippet below.
Reload the log4j file using a web browser:
https://<server_public_url>/<application_context_root>/admin#action=com.ibm.team.repository.admin.reloadLoggingSettings
Click the 'Reload Log Setting' button.
Reproduce the issue.
A file called '<app>-etl-driver.log' will be generated in the folder with the other logs.

log4j.properties file ETL's section after edit:

################################
#            ETL's             #
################################
#Turn off Rational XML JDBC driver logging by default. This is only needed for troubleshooting the ETLs
#log4j.logger.com.ibm.rational.drivers.jdbc.xml=OFF
#log4j.logger.com.ibm.rational.etl=OFF
#Comment the above 2 lines and uncomment the lines below to turn on logging
log4j.logger.com.ibm.rational.drivers.jdbc.xml=INFO, etlDriver
log4j.logger.com.ibm.rational.etl=INFO, etlDriver
log4j.additivity.com.ibm.rational.drivers.jdbc.xml=false
log4j.additivity.com.ibm.rational.etl=false
log4j.appender.etlDriver=org.apache.log4j.RollingFileAppender
log4j.appender.etlDriver.MaxFileSize=10MB
log4j.appender.etlDriver.MaxBackupIndex=5
log4j.appender.etlDriver.File=logs/ccm-etl-driver.log
log4j.appender.etlDriver.layout=org.apache.log4j.PatternLayout
log4j.appender.etlDriver.layout.ConversionPattern=%d{ISO8601} [%30t] %5p %-50.50c  - %m%n