How many digits require a place-value base eight system?

Your question is unclear, but a base 8 number system needs 8 digits, usually 0, 1, 2, 3, 4, 5, 6, and 7.





An example is 74(base 8) = 7*8+4 = 60(base 10)





"Digit" is a bad word to use here, since it implies "10"