My husband is working in Puerto Rico for 6 months this year doing linework-they take out 10% automatically, will the US charge him additional federal tax on that?

Was the tax taken out paid to Puerto Rico on his form W-2?

Yes, he will need to pay US taxes on this income as well.

 "U.S. citizens and resident aliens who aren't bona fide residents of Puerto Rico during the entire tax year are required to report all income from worldwide sources on their U.S. income tax return." https://www.irs.gov/taxtopics/tc901

However, when filing your taxes, there is a tax credit available for taxes paid to a foreign country.  Puerto Rico, even though a US Possession, is still eligible for the tax credit. Foreign Tax Credit US Possessions

To take the Foreign Tax Credit in TurboTax do the following:

1. Click Federal
2. Deductions and Credits
3. Scroll down and click Show More next to Estimates and Other Taxes Paid
4. Click Start next to Foreign Taxes

What if the tax was only taken out on his paycheck stub but does not show up on his W-2, can you still take the credit?
Money was taken out for Puerto Rico tax. But does not show up on the W-2