Where is Careful Aim in the Hunter talent tree?

Marksmanship tree, row 2, column 3. You need 5 points spent in Marksmanship before you can learn it.

Is Careful Aim new in WoW Forever?

Yes. Careful Aim has no Classic 1.12 counterpart.

Rank	Effect	Source
1	Increases your Attack Power by 20% of your Intellect.	client
2	Increases your Attack Power by 40% of your Intellect.	client
3	Increases your Attack Power by 60% of your Intellect.	client
4	Increases your Attack Power by 80% of your Intellect.	client
5	Increases your Attack Power by 100% of your Intellect.	client

Tree: Marksmanship, row 2, column 3. Needs 5 points in Marksmanship first. The earliest you can finish all 5 ranks is level 19 if you put every point into this tree.
Unlocks: Mortal Shots (requires Careful Aim at full rank).
Competes with: Improved Stings, Efficiency in the same row.

Careful Aim is new in WoW Forever. Nothing in Classic 1.12 does this for Hunters.

Beast Mastery Hunter leveling build (10–60) · 5/5
Marksmanship Hunter endgame PvE build (20/31/0) · 5/5
Beast Mastery Hunter endgame PvE build (31/20/0) · 5/5
Survival Hunter endgame build (0/20/31) · 5/5
Marksmanship Hunter PvP build (0/31/20) · 5/5