Answer
The domain of $(f \circ g) (x)$ is $(2,\infty)$
The domain of $(g \circ f)(x)$ is $(0,\infty)$
Work Step by Step
We are given:
$f(x)=\log_{2}x$
$g(x)=x-2$
$(f \circ g) (x)=f(g(x))=\log_{2}{(x-2)}$
$(g \circ f)(x)=g(f(x))=\log_{2}x-2$
The domain of $(f \circ g) (x)$ is $(2,\infty)$ and $(g \circ f)(x)$ is $(0,\infty)$