Formal:
* Quel est le mois? (This is the most direct and formal way)
Informal:
* C'est quel mois? (This is a more casual way to ask)
* On est en quel mois? (This literally translates to "What month are we in?")
Specific situations:
* Tu sais quel mois on est? (Do you know what month it is?) - This is a good option if you are talking to a friend or someone you know well.
It's also important to remember that in French, months are always capitalized.