Unicode characters themselves aren't owned by anyone

The underlying emoji character — its code point and meaning — is part of the open Unicode standard and isn't owned by any single company, similar to how no one owns the letter A.

But the specific artwork usually is

The particular visual design of an emoji — Apple's version, Google's version, Twitter's Twemoji artwork — is typically created and owned by that company or project, and each has its own license terms for reuse.

Twemoji as a commonly used option

Twitter's open-source Twemoji artwork is released under a license that permits broad reuse, including commercial use, provided attribution requirements are met, which is part of why it's a popular choice for third-party apps and websites.

The practical rule of thumb

Before using a specific platform's emoji artwork in a commercial product or marketing material, check that particular design's license terms rather than assuming all emoji art is free to use the same way, since terms vary significantly between Apple, Google, Twitter, and others.