To determine which point lies on the graph of the logarithmic function \( g(x) = \log_9 x \), we can use the fact that \( g(x) \) is the inverse of \( f(x) \).
Since \( f(x) = 9^x \) and the point \( (2, 81) \) lies on the graph of \( f(x) \), we have:
\[ f(2) = 9^2 = 81 \]
This means that for the logarithmic function \( g(x) = \log_9 x \), if \( f(2) = 81 \), then:
\[ g(81) = 2 \]
Thus, the point \( (81, 2) \) lies on the graph of \( g(x) \).
Therefore, the correct response is:
(81, 2)