How can we ascertain that Almighty God is the returned Jesus?

The answer from Almighty God’s word:

“… first, He is able to open up a new age; second, He is able to supply the life of man and show man the way to follow. This is sufficient to establish that He is God Himself. At the very least, the work He does can fully represent the Spirit of God, and from such work it can be seen that the Spirit of God is within Him. As the work done by the incarnate God was mainly to usher in a new age, lead new work, and open up new circumstances, these few conditions alone are sufficient to establish that He is God Himself. …”

from “The Difference Between the Ministry of the Incarnate God and the Duty of Man” in The Word Appears in the Flesh