For interactive testing, follow the directions given in tkconclient.
When scripts are not run interactively but started using e.g. an icon on the Android home screen, script errors may show up in the Android system log buffer when not reported through the Tcl background error mechanism. In this case, the Android Debug Bridge (adb) should be used on a development system. Refer to the description of the logcat command-line tool and see an example output in the last image of the AndroWish SDK documentation.
Output to the stderr and stdout channels in non-interactive scripts is normally not shown, but can be easily displayed, too, when the console window is made viewable using console show.