Knowing only one fact about g(x) limits your options.
since all you know is g(8) = -3,
the only value x for g(x-4) for which you have info is x = 12
-g(12-4) - 6 =
-(-3) - 6 = 3 - 6 = -3
so, the only point you know is on the second curve is (12, -3).