When you enter the United States
Your passport must always be valid at least 6 months into the future.
J-1 visa stamp
A J-1 visa stamp that U.S. consular officials place in your passport allows you to apply to enter or reenter the United States. It does not guarantee admission to the United States nor does it determine your length of stay.
If your J-1 visa expires while you are in the United States
It is not necessary to renew your visa as long as you remain in the country. A visa can be secured only at a U.S. embassy or consulate abroad. Canadians do not require a visa.
I-94 admission record
The electronic record of your I-94, after arrival in the United States, along with a valid Form DS-2019 permits you to stay temporarily in the United States as a J-1 student.
A new I-94 each time you enter the United States
Each time you enter the United States, you will be issued a new I-94 card with a new admission number. The exception is when you reenter the country after visits of 30 days or less to Canada, Mexico, and adjacent islands.
Renewing or replacing your passport
Lost or stolen? Report a lost or stolen passport to the police. Your home country government may require a police report before issuing a new passport.
Renewing or replacing your passport: Contact your country’s consulate in the United States.