A:Answer Hey there!
Unfortunately, the Apple Pencil 2nd generation is not compatible with the first-generation iPad Pro 12.9-inch. The 2nd generation Pencil is only compatible with iPads that have a magnetic charging strip on the side, such as the iPad Pro 12.9-inch (3rd generation and later).
However, the 1st generation Apple Pencil is still compatible with your iPad Pro 12.9-inch. It's a great stylus, and it's much more affordable than the 2nd generation.
I hope this helps! Let me know if you have any other questions. :)