According to a SWISS representative on Twitter, you need to specify the destination country, which in this particular case is the US:
Yes, then it would be the country you're travelling to.
I'm personally not very happy with the lack of common sense in the way the check-in form is composed, but ...
First of all, airlines to their utmost best to ensure that they do not have passengers who need visa but do not have them.
If an airline notice you do not have a needed visa before you enter the plane, they might not transport you at all, or if it is because the travel is re-routed, they might re-route you again, so you are not in the plane.
But if a plane ...