Where in all biblical Greek or secular Greek does the Emphatic position changes a noun from indefinite to definite like a god to God John1:1?

>> They claim the emphatic position changes the a god to the God. <<

I don't know who "they" are
but
clearly you are no expert in Koine Greek
and I doubt that anyone on Y!A is.

I recommend that you refer this question to an expert in Koine Greek.

If not, I recommend you review this SEEMINGLY knowledgeable discussion on the topic.
https://www.ntgreek.org/answers/answer-frame-john1_1.htm

Currently I can't find a more detailed online discussion from any creditable expert (though in the past I have been able to do so; perhaps that web page has been deleted, or simply swamped by all of the non-scholarly pages now available to search engines)....Show more

What in the WORLD are you blathering about??

"They claim the emphatic position changes the a god to the God." ???

Here's the explanation:  

Reversal of the subject noun and predicate noun at the end of a list was a common stylistic practice and is still used today.              


Εν αρχή ήν ο λόγος -- in the beginning was the Word         

καί ο λόγος ήν πρός τον θεόν -- and the Word was with God        

καί θεός ήν ο λόγος -- and the Word was God. 


Got it?  The Word -- the Son -- IS God.  

Samwise -- There's no difficulty.  It's perfectly clear to someone who knows Koine....Show more

Nowhere, as far as I know, but Trinitarians couldn't stomach Jesus not being God or an aspect of God....Show more

The trouble is that the definite and indefinite articles didn't exist in Greek. And the Hebrew term they were discussing in John 10 (a discussion that would have been conducted in Aramaic, not the Greek translation we have) the term translated as "gods" is complex, as Jesus emphasizes by quoting a psalm in which judges are described as "elohim." 
 
I could live with a translation in which we settled for "the Word [Logos] was divine." The verse still says the Logos was "in the beginning," not just "before Abraham." And a few verses later John (or whoever really wrote it) declares the Logos became flesh and dwelt among us, clearly setting out a Christology in which Jesus is an embodiment of something timeless and more than human. 
 
That's the writer's opinion; clearly, opinions among the apostles varied and developed over time, as they talked and wrote of what they knew and had come to believe. That particular opinion is accepted and affirmed by mainstream ("orthodox") Christianity, and is one of the beliefs that defines Christian orthodoxy. 
 
I can live with unorthodox versions of Christianity, and I think Christianity as a whole might have done better had it not devolved into fighting, among those of different views, over which of us is entirely correct. I doubt any of us is entirely correct, and I'm content to wait and see where each of us turns out to be wrong, or right. 
 
What I see as more dangerous is the temptation to declare ourselves right and pick fights with everyone else. When we do that, we emulate the Sanhedrin who engineered Jesus' execution. And Jesus himself spent quite a bit of his preaching time pointing out that particular attitude as a problem....Show more

Best evidence on the matter comes from the original Apostles and disciples, which has been faithfully preserved, via Catholic Tradition. In light of that true context, we have no problem understanding what the Bible actually says and means. Only those who showed up over a thousand years later and invented an entirely new form of Christianity, based solely on their own personal preferences, need to wrestle with issues of that type.  ...Show more