What is the ruling on subscribing to the "Sharekna" service on "Al-Khulasah.com," which allows the subscriber to earn a $6 commission for each person who registers through them, especially given that the website translates and sells summaries of non-Arabic books, after it affirms its ownership of the translation rights and its adherence to Islamic Sharia?

Brokerage is permissible, and the fee is known. There is no harm in the work being unknown, as it falls under the category of ju'alah (a contract for a reward for a specific task). As for multi-level marketing (MLM), it is forbidden because it involves unlawfully consuming people's wealth, contains gharar (excessive uncertainty), and relies on deceiving others and selling them an illusion, where the probability of loss is many times greater than the probability of gain. However, taking a fee for clients who come through you is permissible, provided that what is being sold is not forbidden, and provided that the fee is known.