Ipencil 3rd generation

timothais96 wrote:

Why wont my ipencil 3rd gen pair with my iPad Pro 12.9 2nd gen?

Probably because it doesn't exist.

So far only a first and second generation Apple Pencils have been produced by Apple and only the First Generation Apple Pencil is compatible with a second generation 12.9" iPad Pro.

See here: Use Apple Pencil with your iPad or iPad Pro - Apple Support

There is no such thing as an Apple Pencil 3rd Generation.