Learn Turkish: Jokeri sen mi kullanıyorsun? - Are you the one using the lifeline?

In Turkish, the word right before the verb gets the most emphasis or focus. By moving sen (you) to this pre-verbal spot, the sentence specifically asks 'Are YOU the one using it?' rather than asking a general question about the action.

Why is the question particle mi placed after sen instead of at the end attached to the verb?

The question particle mi usually follows the exact word you are questioning. Placing it right after sen doubles down on the focus, making it perfectly clear that the identity of the person using the lifeline is what you are asking about. If it were at the end (Jokeri sen kullanıyor musun?), the focus would shift to the verb.

Since mi is separated from the verb, why does kullanıyorsun still have the -sun ending?

When the question particle mi is moved earlier in the sentence to focus on a specific word, the personal suffix (-sun) stays attached to the verb. The verb must always agree with the subject, no matter where the subject or the question particle is placed in the sentence.

What does the -i at the end of jokeri do here?