"Is Anna in America or in Germany?"
Translation:Анна в Америке или в Германии?
In normal speech I don't always use it but for the sake of this site I do, just in case
In this case both options are correct. In general there are some cases when you can skip preposition and other when you can't. But I think most Russian natives don't know exactly these rules, it's more of philological question. If you're not sure then it's better to use preposition for each object.