Formal:
* Êtes-vous français(e) ? (Are you French?) This is the most formal way to ask.
* Êtes-vous originaire de France ? (Are you originally from France?) This is a more formal way of asking about someone's origin.
Informal:
* Tu es français(e) ? (Are you French?) This is the informal way to ask, used with friends and family.
* D'où viens-tu ? (Where are you from?) This is a more general question that can be used in both formal and informal situations.
* Tu es né(e) en France ? (Were you born in France?) This is a more specific way to ask about someone's place of birth.
Note:
* Français(e) is used for both male and female, but the ending changes to agree with the gender of the person you are asking.
* D'où is an informal contraction of De où, meaning "from where".
* Originaire means "originally from".
You can also combine these phrases to ask more specific questions. For example, you could ask:
* D'où êtes-vous originaire ? (Where are you originally from?)
* Êtes-vous né(e) à Paris ? (Were you born in Paris?)
Choose the phrase that best suits the context of your conversation.