John 20.28 is no proof that Jesus is god because god and lord are in the nominative case and not the vocative case. Every time Jesus is addressed as Lord in the bible he is addressed in the vocative case of lord (kurie) and never in the nominative case of Lord (kurios). Therefore, Thomas was talking about god and lord to Jesus not addressing Jesus as god and lord. So how was Thomas talking about god and lord to Jesus? He was uttering an exclamation, just as anyone would in that situation. Or it was an incomplete sentence, after all we all utter incomplete sentences. Some scholars believe it was an incomplete sentence, I lean more towards an exclamation but don't rule out an incomplete sentence.
Also, it is asserted by scholars that the nominative is used for the vocative, but I have as yet to see even one clear cut example of the nominative being used for the vocative, so I'm not sure that is correct. Even in mark where Mark uses the nomative when quoting Jesus "my god,my god why has thou forsaken me", it is possible that Jesus uttered one in hebrew, then one in aramaic, and that the utterances where different. one case Jesus is excalming in utter aggony, and not addresssing god with "my god my god", in the luke version which is a translation of the aramaic and not the hebrew, Jesus adresses God in the vocative. So why is one version (Mark) in hebrew, and the other version
(Luke in aramaic? obviously because jesus said it two times once in hebrew and once in aramaic. anybody who speaks multiple languages knows that people often swithch back and forth between those languages, every met a bilingual mexican who didint'? I haven't.