This particular argument is one that requires a thread of its own.
For context, it must be understood that the most important daily prayer for the Jews has always been the "Sh'ma" from Deut. 6:4-5, in which the Jews proclaim the God of Abraham, Isaac, and Jacob as the one true God of Israel:
Deut. 6:4 “Hear, O Israel: The LORD our God, the LORD is one. 5 You shall love the LORD your God with all your heart and with all your soul and with all your might.
It is called the "Sh'ma", because that is the first word in the verse, the Hebrew that is translated, "hear". And the three instances of "LORD" in caps are from the name of God, the Tetragrammaton, YHWH, which JW's know as "Jehovah". But the Jews had a tradition to avoid transgressing the commandment not to take the Lord's name in vain, they simply never said His name, and so would avoid that sin. Whether you agree or disagree with that tradition, that's what happened in history. And so when the Scripture was read out loud, Jews would say "adonai" ("Lord") in place of the name, which resulted in the LXX translation of "kurios" ("Lord"), as well as the small caps "LORD" in many translations today.
Why is the relevant? Paul was a Hebrew of Hebrews, a Pharisee, of the tribe of Benjamin. He undoubtedly recited the Sh'ma daily. It was the Sh'ma that identified the God of Israel as both "Lord" and "God". The term "Lord", when used of Jesus Christ, is a far stronger witness to Christ's deity than many Christians even realize.
So the Old Testament understanding of God was simply that, "Elohim", or "adonai". With the coming of Jesus, the Trinity was revealed to Christendom. And so we have two persons, who each identify as the one true God of Israel. They are not two gods, but one God (for only one God exists). But the Son is not the Father, and the Father is not the Son.
So when Paul was writing to the Corinthians, and having to explain why it's okay to eat meat sacrificed to Artemis (1 Cor. 8), by explaining that false gods are idols, who are "nothing in this world", only one god exists ("There is no God but one"), that hearkens back to his Jewish upbringing, and the daily prayer of monotheism, which proclaims the God of Israel as both God and Lord. But now that Jesus has been revealed, what then?
Paul now gives us an expansion of the Sh'ma, to include both the Father and the Son:
1 Cor. 8:6 yet for us there is one God:
the Father, from whom are all things and for whom we exist,
and one Lord,
Jesus Christ, through whom are all things and through whom we exist.
In the Sh'ma, God is both "God" and "Lord".
In Paul's version, He has both "God" and "Lord".
And he identifies the Father as "God" (without denying His Lordship).
And he identifies Jesus as "Lord" (without denying His godhead/deity).
This is not a denial of Christ's deity.
Nowhere does Paul say, "Jesus is not God". Nor would he.
Both Jesus and the Father are (the one) God.
Both Jesus and the Father are (the one) Lord.
But instead of us every time Paul uses the term, "God", or "Lord", we have to guess which person he means, or he has to explicitly identify which, Paul simply creates a convention. When Paul is referring to the Father, he generally refers to him as "God". When Paul is referring to Jesus, he generally refers to him as "Lord". But neither title denies the other.
My interlocuter asks a good question, "Who did Paul consider Jesus Christ to be?" And that is an excellent question, which answer is not friendly to JW's. Here is what Paul wrote about Jesus in his epistles:
Rom. 9:5 ... the Christ, who is God over all, blessed forever. Amen.
Phil. 2:5 ... Christ Jesus, 6 who, though he was in the form of God, ...
Col. 2:9 For in [Christ] the whole fullness of deity dwells bodily,
2Th. 1:12 ... the grace of our God and Lord, Jesus Christ.
Titus 2:13 ... the glory of our great God and Savior, Jesus Christ,
And this is just the testimony of Paul, and doesn't include the testimonies of Isaiah, John, Thomas, Luke, Peter, the author of Hebrews, or Jesus Himself. Not to mention the apostolic fathers and ECF's which followed.