Note 26 at 2 Tim. 3:8: Jannes and Jambres are only mentioned by name in this scripture. This is referring to the magicians who resisted the miracles of Moses (Ex. 7:11-12, 22; 8:7). The Targum of the pseudo-Jonathan contained these names as the magicians of Egypt. The Jewish Talmud mentions Johana and Mamre which many believe to be the Greek forms of Jannes and Jambres. Jannes was mentioned in the Dead Sea Scrolls (see note 27 at this v. and note 28 at v. 9).

Note 27 at 2 Tim. 3:8: How did Jannes and Jambres (see note 26 at this verse) resist the truth? They turned their rods into snakes, but the rod or snake of Moses ate them up (Ex. 7:11-12). Then they turned water into blood (Ex. 7:22). Finally they caused frogs to come up out of the river Nile (Ex. 8:7).

But when Moses turned the dust into lice, Jannes and Jambres were unable to do so. They told Pharaoh that this miracle was definitely God and not sorcery (Ex. 8:18-19). When Moses brought forth boils on men and beasts (Ex. 9:10-11), the magicians were not able to stand because they had the boils too.

So, Jannes and Jambres resisted Moses' claim that his power was from God. They sought to demonstrate that it was nothing more than magician's tricks or sorcery. In like manner, the men that Paul was speaking about had come into the Ephesian churches and tried to turn people from believing in Paul as their apostle and Timothy as their pastor. They were countering the authority of God's messengers.