The iPad Air2 is not compatible with Apple Pencil - as it lack the screen hardware with which the Pencil interacts. As the required screen hardware is absent from the Air2, this functionality cannot be added by a software update.
Here is the compatibility list for Apple Pencil and iPad:
Apple Pencil (2nd generation)

You can use Apple Pencil (2nd generation) with these iPad models:
- iPad Pro 12.9-inch (3rd generation) and later
- iPad Pro 11-inch (1st generation) and later
Apple Pencil (1st generation)

You can use Apple Pencil (1st generation) with these iPad models:
- iPad Pro 12.9-inch (1st or 2nd generation)
- iPad Pro 10.5-inch
- iPad Pro 9.7-inch
- iPad Air (3rd generation)
- iPad (7th generation)
- iPad (6th generation)
- iPad mini (5th generation)
Not sure which iPad you have? Identify your iPad model.