I am wondering what the object question for this sentence would be:
They are talking behind someone's back.
The question should ask about the person whom they are talking behind their back.
I am wondering what the object question for this sentence would be:
They are talking behind someone's back.
The question should ask about the person whom they are talking behind their back.
Change the noun to a query pronoun: 'someone' -> 'whom' ('who' is for subjects)
Note that the noun is possessive (someone's): 'whom' (or 'who') -> 'whose'
Transpose the subject and verb to form a question: 'they are' -> 'are they' (if the verb is lexical you will need to split it into an auxiliary verb and an infinite verb, and only transpose the first auxiliary: 'they ate' -> 'they did eat' -> 'did they eat', etc.)
Try to front the query noun phrase ('whose back') or the phrase that contains it ('behind whose back') {since some grammarians don't like dangling prepositions}
"Whose back are they talking behind?" or "Behind whose back are they talking?"