Anyone coming to the US should have a passport. You might or might not also need a visa, depending upon the nature of your visit.
No, US citizens do not need a transit visa for the UK if they are passing through the country on their way to another destination.
NO, you need to apply for Transit Visa at the US embassy in Nigeria before you leave Nigeria
flying to usa stop over in transit in heathrow-sa passport do I need a transit visa
Yes, US citizens can obtain a Saudi Arabia transit visa for their travel plans.
No
Yes.
Yes, US citizens need a transit visa for Saudi Arabia if they are transiting through the country for more than 12 hours.
You do not need a transit visa, if you do not go out of the airport to see London or change airports at London.
1) A green card does not mean anything outside the USA. It is your nationality (citizenship) that determines if you need a visa. 2) The UK is not part of the Schengen Area. A Schengen visa is never valid for the UK. You need to ask the UK embassy in the USA (or look on their website) to find out if someone of your nationality requires a transit visa for the UK.
no
Yes you will. Its the US. You need a Visa to enter or pass through the US. Only if you are not coming off the plane.
No, US citizens do not normally need a Schengen visa. They are normally allowed to stay for 90 days as a tourist without a visa.