Where is Champion of the Light in the Paladin talent tree?

Retribution tree, row 6, column 3. You need 25 points spent in Retribution before you can learn it.

Is Champion of the Light new in WoW Forever?

Yes. Champion of the Light has no Classic 1.12 counterpart.

Rank	Effect	Source
1	Increases your spell damage by up to 12% of your Intellect, and reduces the cast time of your Hammer of Wrath by 0.2 sec.	client
2	Increases your spell damage by up to 24% of your Intellect, and reduces the cast time of your Hammer of Wrath by 0.4 sec.	client
3	Increases your spell damage by up to 36% of your Intellect, and reduces the cast time of your Hammer of Wrath by 0.6 sec.	client
4	Increases your spell damage by up to 48% of your Intellect, and reduces the cast time of your Hammer of Wrath by 0.8 sec.	client
5	Increases your spell damage by up to 60% of your Intellect, and reduces the cast time of your Hammer of Wrath by 1.0 sec.	client

Tree: Retribution, row 6, column 3. Needs 25 points in Retribution first. The earliest you can finish all 5 ranks is level 39 if you put every point into this tree.

Champion of the Light is new in WoW Forever. Nothing in Classic 1.12 does this for Paladins.