Learn French: Quelle est votre nationalité ?

D'où strictly means "from where", so it is used when asking about a place, like in D'où venez-vous ? (Where do you come from?). Here, you are asking for a specific thing (a nationality) rather than a location. In French, when asking "what is your [noun]", you use Quel or Quelle.

Why do we use Quelle here instead of Quel?

Quelle means "what" or "which". It changes its spelling to match the gender of the noun it asks about. Because nationalité is a feminine noun, we use the feminine form Quelle. If the noun were masculine, you would use Quel.

Can I say Quelle est ta nationalité ? instead?

Yes! votre is the formal or plural word for "your". If you are talking to a single friend, family member, or child, you would use the informal word ta instead, because nationalité is feminine.

Is there an easy way to remember that nationalité is feminine?

Yes! In French, almost all nouns that end in -té (like nationalité, université, and beauté) are feminine.