Actually, that means : 'What is the premise of your argument?' (!). Moi, je suis citoyen du monde.

Nearly none. Though Odkud jste is = Where are you from. In neither Czech nor English does it have to mean that you were born there. You live there now. You have been living there for 20 years and so that is what you use when people ask you.

Odkud pochazite has more of a meaning = where do you originate from. For a lot of people (and specially Czechs) those two questions are often the same thing.