Is the owner of an internet cafe sinful and his earnings unlawful due to his customers watching songs that include indecent scenes, given his inability to prevent them, and is he required to liquidate the project, and is he sinful if he sells it to someone who will continue the same activity?

If the owner of a project is able to prevent evil acts, then there is no harm in investing in it. However, if he is unable to prevent them, then it is not permissible for him to open the project because that would be aiding in sin, and the money earned from it would be unlawful. The questioner must prevent the use of his devices for evil acts. If he is unable to do so, then he must sell the shop, and there is no sin upon him in that if the buyer will not use it for unlawful purposes.