If a person has both U.S. and EU citizenship (say Germany), and is currently living and working in the EU, pay any taxes on income to the U.S.?
Also, apparently no matter what, the person needs to file U.S. tax returns.
The United States of America is one of the only countries that taxes based on citizenship, rather than residency. In fact, it might now be the only country that does this. (Eritrea also used to, but I believe that this may have changed.)
This means that if you are a US citizen regardless of where you live in the world, you need to pay (federal) tax to the US government, as well as paying tax to the country where you are resident. You do not need to pay State tax, just Federal tax. And there is a threshold of foreign earnings below which you do not need to pay anything (around $100K per year plus or minus a few thousand).
You DO need to file your tax return every year, even if it is just tell the IRS that you did not earn enough to have to pay federal tax.