Let's find the inflection points, we'll need to solve the equation for this
$$\frac{d^{2}}{d x^{2}} f{\left(x \right)} = 0$$
(the second derivative equals zero),
the roots of this equation will be the inflection points for the specified function graph:
$$\frac{d^{2}}{d x^{2}} f{\left(x \right)} = $$
the second derivative$$\frac{- \frac{\frac{x^{2}}{x^{2} + 1} - 1}{\sqrt{x^{2} + 1}} - \frac{2}{\sqrt{x^{2} + 1}} + \frac{2 \sqrt{x^{2} + 1}}{x^{2}}}{x} = 0$$
Solve this equationSolutions are not found,
maybe, the function has no inflections