If not specified, which encoding/code-page does tMomOutput use?
tMomOutput will use the default encoding of the machine/locale where the Job is running.
If you don't want to use the default encoding, then you can overwrite it as follows:
Select the Advanced settings tab of tMomOutput.
Select the Set MQMD Fields checkbox.
Click the green + sign to add a field.
Click the Field Name column to select characterSet.
Set the Field value of the encoding value you want.