To translate the point \((2, -5)\) to \((2, -6)\), we notice that the x-coordinate remains the same (2), while the y-coordinate changes from \(-5\) to \(-6\).
This represents a downward shift of 1 unit in the y-direction. Therefore, we need a function that takes \(y\) and subtracts 1 to achieve the change in the y-coordinate.
The function that accomplishes this is:
\[ g(y) = y - 1 \]
This function takes any y-value and reduces it by 1, which corresponds to the downward translation observed.
So, the correct answer is:
D. g(y) = y - 1.