Jenkins Junit plug-ins works very well with TestNG, but not the junit-attachments plug-ins.

Junit plug-ins is able to show the console output in master when a test fail even if executing testng.

But junit-attachments plug-ins is making the thing complicated by requiring real file created that contain the output.

The plug-in is looking for path/file like:
c:\jenkins\workspace\SIT3_OPS_Smoketest_Functional_Tests\functional-tests\target\surefire-reports\junitreports\com.onassignment.ops.tests.company.CompanyTests-output.txt

But those files doesn't exist.

Again, to be clear, the core junit plug-ins is able to grab the output stream from the slave, so I don't see why the attachment plug-ins find it hard to do so.

We do have a file having the entire output at that location: C:\jenkins\workspace\SIT3_OPS_Smoketest_Functional_Tests\functional-tests\target\surefire-reports\TestSuite-output.txt

That file may be created only with <redirectTestOutputToFile>true</redirectTestOutputToFile>, this should not be needed at all. Jenkins core Junit plug-ins is working very fine without this setting to true.