Field help:
16. a) Tax-free wages under DTA
Enter the amount from line 16 a) of your employment tax statement:
"Tax-free wages under double taxation agreements (DTA)"

If you enter an amount here, you must provide additional information about your employment abroad. The form N-AUS ("Foreign income from employment") is also part of your income tax return.
You can enter the required information in the "Weitere Einnahmen" section.