YOU SAID:

whom'st's man's is this's

INTO JAPANESE

誰のものがこれです

BACK INTO ENGLISH

Whose stuff is this

INTO JAPANESE

これは誰のものなの？

BACK INTO ENGLISH

To whom is this?

INTO JAPANESE

誰がこれですか。

BACK INTO ENGLISH

Who is this?

INTO JAPANESE

これは誰です？

BACK INTO ENGLISH

Who is this?