In connection with Rev 20:4 ("the word of God" vs. "speaking about God"), there is an interesting thematic thread running through Revelation that might explain what is meant by "the word of God":
Rev 1:2 . . . [John] bore witness to the word God gave and to the witness Jesus Christ gave . . .
Rev 1:9 . . . because of the word of God and the testimony about Jesus . . .
Rev 6:9 . . . because of the word of God and because of the witness work that they used to have . . .
Rev 12:17 . . . who observe the commandments of God and have the work of bearing witness to Jesus.
Rev 14:12 Here is where it means endurance for the holy ones, those who observe the commandments of God and the faith of Jesus.
Rev 19:10 . . . you and of your brothers who have the work of witnessing to Jesus. Worship God; for the bearing witness to Jesus is what inspires prophesying
Rev 20:4 . . . those executed with the ax for the witness they bore to Jesus and for speaking about God [lit. the word of God].
Comparing these verses which use a similar formula for describing Christians, I would venture that "the word of God" is equivalent to Rev 12:17, "observe the commandments of God." The rendering, "speaking about God," would seem to take it in a different direction. (Although, to be fair, at least one other translation, the NLT, has something similar to the NWT - see here)