Is working as a customer service representative for an application, a section of which – unrelated to the enquirer's direct work – contains stores that sell pork, and where the enquirer sometimes directs customers to this section without knowing the details of their requests, considered forbidden and does it make the money earned from it illicit?

If your work is permissible, then there is no harm in it for you, and explaining how to contact the marketing department for customers does not affect it, because marketing is not limited to selling pork. Therefore, as long as you do not know the customer's intention in purchasing something forbidden, there is no harm in guiding them to the marketing department, and the sin is on them if they purchase something forbidden.