To evaluate the expression \( \log_2(2^8) \), you can use the logarithmic identity:
\[ \log_b(b^x) = x \]
Here, \( b \) is the base of the logarithm (which is 2 in this case), and \( x \) is the exponent (which is 8 here).
Therefore,
\[ \log_2(2^8) = 8 \]
So, the answer is:
8