Formal:
* J'ai commencé ? (Have I started?) - This is the most direct and literal translation.
* Ai-je commencé ? (Have I started?) - This is another grammatically correct way to ask the question.
Informal:
* J'ai déjà commencé ? (Have I already started?) - This emphasizes that you're wondering if you've begun the task at hand.
* J'ai commencé, non ? (I started, didn't I?) - This is a slightly more casual way to confirm that you've started.
Other options:
* Est-ce que j'ai commencé ? (Did I start?) - This is a more neutral way to ask the question.
* J'ai pas encore commencé, non ? (I haven't started yet, right?) - This clarifies that you haven't started yet.
The best way to choose the right phrase depends on the context of the conversation and your relationship with the person you're talking to.