The Hong Kong flag emoji is represented by the regional-indicator sequence for Hong Kong.
Flag emoji for many countries and territories are created from two regional indicator symbols corresponding to a two-letter geographic code. The sequence for Hong Kong uses the letters H and K, displayed as regional indicators rather than ordinary alphabetic characters.
The resulting artwork is supplied by the platform, so the flag’s exact design can vary slightly between operating systems. Unicode encodes the sequence, but it does not require every vendor to display it identically or support it at the same time.
Hong Kong is a special administrative region of China, and its flag emoji is distinct from the emoji flag for China. Macau also has its own regional-indicator sequence, which is why these nearby territories can be confused in lists of flag emoji.