Answer
$\log_8{2}=\frac{1}{3}$
Work Step by Step
Write the radical in exponential form to obtain:
$8^{\frac{1}{3}}=2$
RECALL:
$a^x=y \longrightarrow \log_{a}{y}=x$
Use the rule above, with $a=8$, $x= \frac{1}{3}$, and $y=2$, to obtain:
$\log_8{2}=\frac{1}{3}$