Is promoting an online oil stock exchange trading company permissible, and what is the ruling on the money earned from it, given that the company claims to operate in an Islamic manner and does not disclose trading details until after registration?

If the company adheres to Sharia controls in trading oil on the stock exchange, then there is no harm in promoting it. Otherwise, it is not permissible, because it involves assisting in sin, and merely advising people to refer to Sharia fatwas does not absolve one of sin. The profits gained must be disposed of, in proportion to the forms of prohibited trading they contain.