The general ecu.test log files are in your temporary directory.
For a quick access you can enter %temp% in your Windows Start menu and navigate to your respective ecu.test version directory.
There you will find ECU_TEST_ERR.log  and ECU_TEST_OUT.log. If you use test management service you will find a TMS.log  as well.

If you use Tool-Server you will find Tool-Server_ERR.log  and Tool-Server_OUT.log.

Whenever you execute a test, ecu.test will generate specific ECU_TEST_ERR.log  and ECU_TEST_OUT.log in the same folder as the test report (.trf)

The general test.guide log files are stored in your test.guide workspace directory: ~test.guide_WORKSPACE~\TTS-TM\logs

Take a look at your test.guide instance and navigate to Info > Help contents > 8.1. Working with logs.

Please log into Jenkins and navigate to the failed build.
Select Console Output > View as plain text and copy the whole text into an editor and save it as a .txt file.