YOU SAID:

I don't know who is on first

INTO JAPANESE

私は誰が最初にいるのか分からない

BACK INTO ENGLISH

I don't know who's first.

INTO JAPANESE

誰が最初なのか分からない。

BACK INTO ENGLISH

I don't know who's the first.

INTO JAPANESE

私は誰が最初なのか分かりません。

BACK INTO ENGLISH

I don't know who is the first.

INTO JAPANESE

私は誰が最初なのか分かりません。

BACK INTO ENGLISH

I don't know who is the first.