In accordance with the Securities and Futures (Contracts Limits and Reportable Positions) Rules, no person, other than a person who is authorized by the SFC or under the rules of recognized exchange company, may hold or control futures contracts or stock options contracts in excess of the prescribed limit (“Position Limits”).  Any person who beneficially holds or controls open positions in excess of the reporting level, is responsible for filing a Large Open Position Report with HKEX (LOP Reporting).

LOP Reporting Levels and Position Limits may vary by products.  The complete list of LOP Reporting Levels and Position Limits can be found in the HKEX website

https://www.hkex.com.hk/services/trading/derivatives/overview/trading-mechanism/large-open-positions-and-position-limits?sc_lang=en

An Exchange Participant, who is aware or made aware of a breach of position limit by its client, should immediately: (a) notify the Exchange, and (b) request the client to liquidate the excess position.

An “ultimate beneficial identity” (or ultimate client) is a person who holds the positions with beneficial ownership, while a “transaction originator” is a person who is responsible for originating instructions for transactions on behalf of the other person (e.g. a fund manager). If positions are held or controlled by a single ultimate client in more than one individual and/or corporate account, should must be aggregated for LOP reporting purpose.

The responsibility lies with the persons in control of the reportable positions, who is the transaction originator and the ultimate beneficial owner of the positions.

You can choose to submit the LOP report to HKEX directly or through your broker. In the event you hold a reportable position in more than one account with multiple brokers. You may instruct any one of your brokers to report your total positions to Exchange. Alternatively, you can ask all your brokers to separately report positions in each of your accounts to the Exchange.

The underlying assets of stock options are individual stocks traded on SEHK. However, not all stocks traded on SEHK are eligible to be underlying assets of stock options. Please refer to the Stock Option Class List in SEHK website:

https://www.hkex.com.hk/eng/prod/drprod/so/classlist_so.htm

The strike price is the price at which the option buyer and seller agree to trade the underlying stock, if the option is exercised. A call option whose strike price is below the price of the underlying stock is in-the-money. Such an option allows the holder to buy the shares for less than the current market price. A call whose strike price is above the underlying stock's price is out-of-the-money. Conversely, a put whose strike price is above the underlying stock's price is in-the-money. This means the put holder can sell the stock for more than its current price. A put whose strike price is below the underlying stock's price is out-of-the-money. 

Stock options have an exercise period which limits their validity. After the expiry day of that exercise period, the option can no longer be traded or exercised. There are conventionally two categories of options in relation to exercise - American style and European style. An American style option can be exercised any time from its issuance up to its expiration. A European style option can only be exercised on the expiration day. An American style option offers more flexibility to its holders in terms of exercise; therefore it can command a higher premium than its equivalent European style option. At the date of this publication, stock options at HKEx were all American style. The expiry date is the trading day immediately preceding the last trading day of an expiry month 

Call options that have a strike price higher than the price of the underlying stock or put options that have a strike price lower than the underlying stock's price are regarded as out-of-the-money and have no intrinsic value, but they have time value. 

More information about Hong Kong Stock Options Contract Specifications, please refer to below

link: https://www.hkex.com.hk/products/listed-derivatives/single-stock/stock-options?sc_lang=en