Without a legitimate license, you cannot contact VMware/Broadcom support for troubleshooting. Furthermore, as an EOL product, new hardware (CPUs, storage controllers, network cards) is not certified for use with ESXi 5.5. Even if you find a key, you may be unable to install it on modern servers.
That said, I can write a that addresses what users might actually need when searching for this term – whether it's understanding licensing, finding legitimate alternatives, or troubleshooting older systems. vmware esxi 55 license key 14k
Mastering VMware vSphere 5.5: Architecture, Licensing, and Legacy Enterprise Management Without a legitimate license