Here's the logic board. At the top are highlighted the Apple APL1021 A9X 64bit processor (red), SK Hynix H9HCNNNBTUMLNR-NLH 16Gb (2GB) LPDDR4 RAM (2x orange highlights), Toshiba THGBX5G8D4KLDXG 32GB NAND Flash (yellow), InvenSense MP67B 6-axis gyroscope-accelerometer combo (green), NXP 65V10 NFC controller (lighter blue), NXP LPC11U37 ARM Cortex-M0 microcontroller (darker blue) and Apple (Cirrus Logic) 338S1213 audio codec (magenta). Shown on the same board at the bottom are Fresco Logic FL1100 4-port USB 3.0 host controller (red), Universal Scientific Industrial 339S00045 WiFi module (orange), NXP 1610A3 (yellow; also in iPhone 6s/6s Plus), 343S00025-A1 (green), 343S00052-A1 (lighter blue), Maxim's MAX98721CEWV (darker blue) and Fairchild's FDMC 6683 (magenta). Source: iFixit.
On the back of the display, there are 2 of Broadcom BCM15900B0's, NXP's 8416A1 Touch ID sensor, Parade Technologies DP695 timing controller and TI's TPS65144. According to Apple this is a DP665 LCD timing controller from the iMac Retina 5K modified to support the display's variable refresh rate. Source: iFixit.
The iPad Pro has 2 two antennas that use MIMO for 802.11ac WiFi speeds of up to 866Mbps and LTE speeds of up to 150 Mbps. Source: iFixit.