Is money earned from working in a café considered unlawful gain?

If your work in this coffee shop involves preparing or serving impermissible items such as tobacco smoke (cigarettes) and the like, then it is not permissible, because it constitutes cooperation in sin and aggression. Therefore, the salary you receive would be unlawful, as it is a wage for an impermissible benefit. However, if your work involves permissible items, such as preparing and serving tea and coffee, then it is permissible.