If I have a dog at my house (live with parents) and they are strict on keeping the dog. The dog goes on the couch and sometimes even eats snacks there so there must be najis on the couch but I don’t know where. Should I completely avoid sitting there or because I doubt where it is there’s no isssue

Ustadh AbdulAziz al-Haqqan

Yes avoid sitting there and you already know that it regularly eats there and that is knowledge. Also you already know if it drools on it or not.