The Python library is only 400 lines, so reimplementing it in C++ shouldn’t be too hard. Look at the source:
https://github.com/pimoroni/skywriter-hat/blob/master/python/library/skywriter.py
You can controll the GPIO through sysfs and do I2C communication via Linux i2c_* calls. You might get inspiration for the later by looking at the source for backlight.c.