Jonathan said: that he was not simply talking to God in those verses as the JWs falsly teach.
nark: Actually JWs do not teach that. They have occasionally resorted to that explanation in the past but generally the WT admits that "my God" is addressed to Jesus, only in a weak or derived sense.
By "talking to God" I mean "directed to God," and their idea that Thomas was somehow talking to Jesus but actually directing that talk to God is just more convoluted hair-splitting double-speak on their part. If you talk to someone while standing in their presence can you really be directing that to someone else? Doesn't seem reasonable since it says Thomas was answering Jesus (John 20:26-29). He wasn't answering the heavenly Father.
They teach it "may" have been "directed to God," pursuant to the Reasoning book and/or Should You Believe in the Trinity tract." As you know the Jehovah's Witnesses teach that Thomas thought of Jesus as no more than a special human occupying a “position far higher” than men and judges who were addressed as “gods” in the Old Testament (see John 10:34, 35 RS; Ps 82:1-6) (Reasoning, 213). Thus, Jesus was “like a god” (Should You Believe, Chapter 9).
As just mentioned, they also suggest “that Thomas may simply have made an emotional exclamation of astonishment spoken to Jesus but directed to God” (ibid.) none of which makes sense, particularly in light of Psalm 35:23 and John 1:1 which the Catholics regard as "a literary inclusion with the first verse of the gospel: “and the Word was God” (NAB notes John 20, 28).
In either event they deny that Thomas thought of Jesus as "God" but the sum of evidence suggests otherwise given the fact that Jesus said He would resurrect Himself, and he stood before Thomas resurrected. Hope that clarifies what I intended to say.