You can say also "Τίνος είναι τα παπούτσια;" , if I understand right your question.
I was wondering why it wouldn't be τινά είναι τα παπούτσια, for example.
That needs a grammatical explanation based on the declension of the word "τι" (what) . What you can use on the above phrase are two forms of that word (in genitive case):
Τίνος είναι τα παπούτσια; (singular)
Τίνων είναι τα παπούτσια; (plural)
Τινά is not possible in any case...It is only used in idomatic expressions like:
Δύο τινά συμβαίνουν εδώ. (Two possible things may happen here)
Oh, so τίνος is just the genitive form of τι? Okay, that's what I was missing. Thanks!
There is no plural τίνων. Τίνος is a fossil word from Ancient Greek. Modern Greek use more the word ποιανού, ποιανής, ποιανού and plural ποιανών, or even ποιού, ποιάς, ποιού and in plural ποιών for the English whose, which also a genitive fossil word.