Whether you add the -e to "français" does not depend on the word "nationalité" in this case, it depends on the gender of the subject. f you're a boy, you say "Je suis français/Français." If you're a girl, you say "Je suis française/Française." Then it's up to you whether you write it with a capital letter or not. With a capital letter your referring to the noun "Frenchman", and without it you're referring to the adjective "French".

And note that the question word should be 'Quelle..?' with a 'u' in it. Just like in English, you can't have a 'q' without a 'u' after it!

ah!