Why do cats scratch sofas?
First, when a cat's nails grow long, it will scratch furniture such as sofas to sharpen its claws. So, to prevent the cat from scratching the sofa, you can trim the cat's nails regularly, but do not perform nail removal surgery.
Secondly, if the cat scratches the sofa, you can spray the cat with water. We all know that cats are afraid of water. If you do this a few times, the cat will learn that if it scratches the sofa, it will be sprayed with water. Eventually, the cat will give up scratching the sofa. 
Third, cats are very sensitive to certain smells. If you spray a smell that the cat dislikes on the sofa where it often scratches, the cat will stop scratching the sofa. For example, the smell of orange peel and lemon, as well as floral water and medicated oil, are also very disliked by cats.
Fourth, scratching is a cat's natural instinct. You can buy a special scratching post for your cat. You can also use catnip to encourage your cat to scratch on the scratching post, so that your cat won't always scratch the sofa.
