the answer is grammatically wrong and should be 'Whom is it by' or 'By whom?'.
'Who is it by' is probably more common in spoken English even if technically wrong. But the primary answer should be 'By whom?'
Yes, should be by whom.
If using who, it's "Who (verb)"
Kalau "from what" kok salah yaa
From = Dari. What = apa.