問題は、誰が

the question is who

→ 問題
phrase Rare #38,052
the question is who Introduces a question about which person will do something. 問題は literally means “the problem is,” but “the question is” is often more natural in English.
JA: 問題は、誰がこの仕事を引き受けるかだ。
EN: The question is who will take on this job.

問題は、誰がトムの代わりにそこに行くだよ

The question is who will go there instead of Tom.

問題は、誰がトム真実を告げる

The question is who will tell Tom the truth.

問題は、誰がトムのためにそこに行くだよ

The question is who will go there for Tom.

問題は、誰がトム言うのかってことだよ

The question is who’s going to tell Tom.