YOU SAID:
when was the last time anyone saw him?
INTO JAPANESE
誰が彼を最後に見たのはいつですか?
BACK INTO ENGLISH
When was the last time you saw him?
INTO JAPANESE
彼を最後に見たのはいつですか?
BACK INTO ENGLISH
When was the last time you saw him?
That didn't even make that much sense in English.