Percentage of digits in n that are even
There is a serious error in your code. If the function is called as even_digits(0), then it causes the following error:

ZeroDivisionError: integer division or modulo by zero


since in the first if you divide by count which is 0.

So, before improving the code, you should check if it is correct.

ADDED:

THE CASE OF n = 0

It is interesting to understand what should be the result in case the input (that is n) is 0. 

The problem is labeled as: 


  Percentage of digits in n that are even


and the natural interpretation is:


  Percentage of digits in the decimal representation of n that are even


So, what result should give the function when provided with the value 0? I argue it should be 1, since every decimal representation of 0 has only zeroes as digits, so it has a 100% even digits.