Where is Iron Creed in the Paladin talent tree?

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

Is Iron Creed new in WoW Forever?

Yes. Iron Creed has no Classic 1.12 counterpart.

Rank	Effect	Source
1	Increases the threat generated by your Holy Strike ability by 10%. While Righteous Fury is active, Holy Strike also reduces your damage taken by 2% for 6 sec.	client
2	Increases the threat generated by your Holy Strike ability by 20%. While Righteous Fury is active, Holy Strike also reduces your damage taken by 4% for 6 sec.	client
3	Increases the threat generated by your Holy Strike ability by 30%. While Righteous Fury is active, Holy Strike also reduces your damage taken by 6% for 6 sec.	client

Tree: Protection, row 6, column 3. Needs 25 points in Protection first. The earliest you can finish all 3 ranks is level 37 if you put every point into this tree.

Iron Creed is new in WoW Forever. Nothing in Classic 1.12 does this for Paladins.