[Python 3.5][1]Python 3.5, 39 bytes
lambda n:{*map(chr,range(32,127))}-{*n} [Try it online!]Try it online!
Turns input into a set, and remove it from the set containing all ascii characters [1]: https://docs.python.org/3/ [Try it online!]: https://tio.run/##K6gsycjPM/6fZhvzPycxNyklUSHPqlorN7FAIzmjSKcoMS89VcPYSMfQyFxTs1a3Wiuv9n9BUWZeiUaahpJHak5Ovo5CeH5RToqikqbmfwA "Python 3 – Try It Online"