How to know what i am not supposed to eat when i'm coughing?

Cough: Avoid any food which worsens cough. If you are allergic to anything- avoid.Drink enough fluid. Stop smooking if you have habit.

Reason for cough.: It would really depend on why you're coughing. For example, if you're coughing because of gastroesophageal reflux disease, there's a whole litany of dietary recommendations. If you're coughing due to allergies, it may not matter what you eat.