We would need more information to answer your question. U.S. citizens and resident aliens pay tax on worldwide income.
It sounds as if you are a nonresident. In that case you should be filing Form 1040-NR. TurboTax does not support this form. You can use Sprintax.com, an awesome TurboTax partner, to prepare a nonresident return.
Capital gains are taxed at the source, meaning a nonresident will only pay tax on capital gains if the nonresident’s “tax home” is in the U.S. It’s possible you will not have to file a U.S. income tax return. Sprintax.com can help you.
These references may be helpful:
The Taxation of Capital Gains of Nonresident Alien Students, Scholars and Employees of Foreign Gover...
What income is taxable for nonresident aliens in the US?
