Hello 
I need to print elements in system console. On the internet there is information only about running tests from console and printing variable to Katalon console (Print the values of a variable in console).
I tried to use: System.Console.out.println(‘aaaa’) with the new test case but it didn’t work.
Here is the message from Katalon console (test is stopped with Error):
Can anyone help? 
Not this.
Just try
println "aaaa"
Indeed, in that way elements are displayed in the Katalon console.
But, I would like to have data in the external console (out of Katalon Studio).
Do you know how to do it?
Simply impossible.
println "aaa" is just equivalent to System.out.println("aaa"); and the character stream emitted by this statement is directed to Katalon Studio’s Console tab and consumed. The stream is not directed to the “Terminal” outside KS. It is impossible for users to change this configuration.
The easiest alternative for you would be writing text messages into a file, e.g messages.txt. Once your test finished and you got a file, then you can do in the console:
$ cat messages.txt
Do you want to redirect your messages from Katalon Studio to somewhere else, e.g, Fluentd ? It would be a completely new requirement that requires Katalon’s developers involved. User’s can do nothing.