What is the ruling on working in a shop whose merchandise comes into contact with impurities such as human and cat urine? Is the income earned from it lawful? And how should one pray in work clothes?

You are afflicted with waswasah (obsessive whispering), and you must avoid these whispers and pay no heed to them. The ground and whatever is connected to it, such as trees and buildings, become purified by dryness, sun, and wind. This is the view chosen by Shaykh al-Islam Ibn Taymiyyah. So, if ceilings become impure as mentioned, they are purified by drying in the sun and wind, or by rain falling upon them. Rain, if it separates without being altered by impurity, is pure. The default state of things is purity, and a ruling of impurity is only made with absolute certainty, not with doubts and delusions. There is no blame upon you in working or praying, and your salary is lawful. There is no need to indulge these satanic delusions.