f(g(x)) is obtained replacing x = g(x) into f(x) as follows:
[tex]f(g(x))\text{ = }\frac{1}{x-2+5}=\frac{1}{x+3}[/tex]
The domain of a function is the set of all possible values of x.
Given that you can't divide by zero, then
x + 3 ≠ 0
x ≠ 0 - 3
x ≠ -3
