Smallest 8 digit even number

Assuming you're not accepting answer like "00000024", and so you want an "actual" 8 digit number, the answer is

10 000 000

i. e. 1 followed by 7 zeroes, i. e. 10 millions. In fact, it is an even number (it ends with zero), and any number less than this has less than 8 digits:

10 000 000 - 1 = 9 999 999

which has 7 digits.