It depends on what kind of negative SEO. Usually I would not do anything.
like a 301?what about when some "good competitors" added backlinks that redirects to porn?
Can I know how it recognize? On which factor it will take for consideration? Does this apply for every negative SEO?Dont do anything. Google recognizes these attacks and most likely your rankings wont suffer. Use the disavow tool as the last resort if other options fail.
Disavow tool is not 100% safe to use.