I'm going to argue that "I don't know whose mom it is" is the correct word order here. The word order of "whose mom it is" should be the same as in an affirmative statement, as this is the grammar rule in English for word order following phrases like "I don't know." e.g. We say "What time is it?' but: "I don't know what time it is."
In English, it can be either. Or "this is" as a 3rd alternative.
"It" does not refer directly to the person, but rather is a kind of token or place-holder loosely defining the situation (which is "not knowing"). This particular usage in English is far from being grammatically logical, and "she" would certainly be logical and clearly descriptive of the person - but speakers of American English use "it" like this all the time.
This is a very weird sentence. Did someone leave a mom unattended here? Come pick your mom up, please. Weird.
Think genealogy. Or a crime drama, where a woman is discovered to have recently given birth, but nobody knows where the baby is.
I think that would mean - whose this mother - which doesn't make sense
"I don't know whose mom this is" sounds natural if you imagine a PTA meeting with a lot of moms
For non-American English speakers, "PTA meeting" means a meeting of the "Parent-Teachers Association", an informal group of parents and teachers who meet to discuss or help with school functions, to be more fully informed about school programs, etc.
I agree, but imagine a situation where someone is showing his mom in a picture and saying "It is my mom over here". In this kind of cases it is possible to use "it" with a person.
We would use "that" instead of "it". My mom would be so insulted if I ever, in any ircumstance, referred to her as "it".
this is such an unnatural sentence in English. referring to a mother as an 'it' - no one would ever utter this sentence.