Is Nikolai Gogol's stories in the public domain?

It's still under copyright in Saint Vincent and the Grenadines (until 2013), Colombia (2018), Spain (2018), and Mexico (2038). Everywhere else, the copyright has lapsed.However, special legislation...

Yes, but certain expressions of the stories may have their own copyrights.

Yes, although certain adaptations and editions may be protected.

In terms of intellectual property "public domain" refers to items that have no restrictions of use due to expiration of legal controls (patents, trademarks, copyright)

Pubic domain occurs naturally when a copyright expires. In theory, a copyright owner can intentionally disclaim any power to enforce a copyright, making it as if it were "public domain".