I'm interested in processor architecture, and assembly programming, but I can't seem to find any documentation, or even the datasheet on the CPU of the Pi 2 (BCM2836). The document I'm looking for should describe all the registers, instructions, architecture/pipelines etc of the CPU
I'm not surprised you couldn't find any information.
The BCM2836 is a SoC not a CPU. As far as you are concerned the BCM2836 is identical to the BCM2835 except for the different ARM CPU.
The main user CPU used on the Pi 2 is an ARM Cortex A7 with four cores.
If you search for BCM2835 and the ARM CPU you'll find all the information you could need.
The GPIO between Pi and Pi2 are not on the same addres. This link will be help you.