Calculate measurement accuracy of voltage divider with suppressor diode?
Your best guess is probably to take the typical curves from the datasheet and shift them downward by taking into the worst-case numbers where (i.e. at the current) the latter are available. If they're far from your operating point, try to pick a part that's better specified for your application. Then add a safety margin, because extrapolation is a blood sport. 

But basically, I'd suggest avoiding this circuit entirely in most cases. There's not enough information to suggest a better one, but almost anything else that works is better than using a low-voltage zener to clamp an input signal. The zener tolerance at Iz is just the start of the problems.