you need to install the headers and build essentials:
sudo apt update
sudo apt install raspberrypi-kernel-headers build-essential

run to build:
make

run to install:
sudo insmod inky-impression-btn-driver.ko
or
for dkms: make install

run to uninstall:
sudo rmmod inky_impression_btn_driver
or
for dkms: make uninstall

all buttons will be reported inside:
/sys/inky-impression/buttons

and each individual button will be reported inside:
/sys/kernel/inky-impression/btn_a
/sys/kernel/inky-impression/btn_b
/sys/kernel/inky-impression/btn_c
/sys/kernel/inky-impression/btn_d