The answer in church is just Ja. You can't say Jag gör in Swedish, that sounds wrong. The natural way of expressing that would be Det gör jag. 'gör' needs to have some kind of object, and if there isn't one, one can always use det.
Why is "My answer is "yes" " marked as wrong? Even if Swedish doesn't use quotation marks (I don't know either way), it is proper in English to use them. I put "yes" in quotation marks since it's as if the speaker is quoting themselves.