Answer
$\{x|x\ne-4,0\}$.
Work Step by Step
Step 1. Domain of $g(x)$: $\{x|x\ne0 \}$.
Step 2. For $(f\circ g)(x)$: $g(x)-1\ne0 \Longrightarrow -\frac{4}{x}-1\ne0 \Longrightarrow x\ne-4$.
Step 3. Thus Domain of $(f\circ g)(x)$: $\{x|x\ne-4,0\}$.