His sponsor is forcing him to do work that has nothing to do with his profession; can he take something from him in return for that without his knowledge?

It is not permissible for the boss to force the worker to do anything except what was agreed upon in the written or verbal work contract, because Allah, may He be exalted, says (interpretation of the meaning): {O you who have believed, fulfill [all] contracts} [Al-Ma’idah 5:1].

And the Prophet (blessings and peace of Allah be upon him) said: “The Muslims are bound by their conditions.” Narrated by Abu Dawud (3594); c lassed as sahih by al-Albani in Sahih Abi Dawud.

The worker may refuse to do that, or demand payment for the additional work. If the boss refuses, then the right thing to do is to quit the job, or refer the matter to the authorities.

As for payment, if he takes something from the wealth of the sponsor, it is not permissible to do that without his knowledge, because that is deceit and a betrayal of trust.

If he accepts payment from the clients of the company, as appears to be the case from the question, then that is a gift to a worker, which is also haram.

And Allah knows best.