You should report the gross interest amount. If you paid any foreign tax on this interest, you can claim it as a foreign tax credit on form 1116.
How to report this form 1116 in turbotax please?
Please read this TurboTax FAQ: <a rel="nofollow" target="_blank" href="https://ttlc.intuit.com/replies/3302405">https://ttlc.intuit.com/replies/3302405</a>