You can do the paper that others have done again, but it can't be exactly the same as others. You can do it in different ways. You must be innovative and use methods that others have never used. This is like doing an application problem in high school. There are many solutions to the same problem. Although the answer is the same, the process is completely different. The same is true for graduation thesis. As long as your problem-solving process is innovative, you can also do other people's problems.