Formal:
* D'où vient-il ? (This is the most common and formal way to ask.)
Informal:
* Il vient d'où ? (This is a more casual and common way to ask.)
* C'est d'où qu'il vient ? (This is even more informal and commonly used in spoken French.)
With a specific place in mind:
* De quel pays vient-il ? (Where is he from? - Referring to a country)
* De quelle ville vient-il ? (Where is he from? - Referring to a city)
Remember:
* The French word for "from" is "de" and it can be placed before or after the verb "venir" depending on the construction of the sentence.
* The pronoun "he" is "il" in French.
* The verb "to come" is "venir" in French.
Choose the expression that best suits your context and level of formality.