IPad Air 2 . Auto rotate button location?

There is no screen lock rotate button on iPads any longer, starting with the iPad Air 2 and newer iPad models.

You use a software button located in the iOS Control Center panel, now.

The screen rotation lock software button has a label that looks like a circular arrow with a padlock symbol inside of it.

Good Luck to You!

Depends.

What iOS is the iPad running?

On the Home screen, do a single finger swipe down from upper right hand of the screen just under the status bar.