Following some basic information:
Income:36.500,00USD
Fed. Tax: 4900,00USD
State Tax: 1890,00USD
Trainee at a private company.
German citizen.

Do I have to pay Fed. Taxes? The German American Chamber of Commerce California told me that I get the entire amount back..?
Can somebody confirm that or give me different advice?
Thanks in advance!

If you are under a J-1 visa, you are exempt from Social Security and Medicare taxes.

However, as a trainee, you ARE liable for state and federal INCOME taxes.