iPad Pro Touch Filter
There is a very common issue on the iPad Pros (Specifically the 12.9" 1st and 2nd Generations) where if the LCD/Digitizer Flex is unplugged without disconnecting the battery connection, a Filter corresponding with touch will blow and needs to be replaced to restore touch functionality.
Disconnect battery, check for continuity on Filter next to small capacitor as shown in the second image.
If no continuity, Filter/Coil is blown. Replace with a Coil with rating of 240ohms-350ma. Or take coil from Donor iPad Mini 1 like in the last image.