Question

Given: f(x) = 1/x (<- that’s division sign btw)

Answer 1

To evaluate $(g \circ f)(0)$, you'd start by rewriting this as $(g \circ f)(0) = g\big(f(0)\big)$ and your first step of evaluation is to evaluate $f(0)$.

When you evaluate $f(0)$, you have the following:

    $f(0) = \dfrac{1}{0}$

and this is undefined.  Since you cannot perform the first step of the evaluation, you cannot evaluate $(g\circ f)(0)$.