Quora has a policy on self-plagiarism, as part of its policy on plagiarism:
Quora’s strong preference is for people to use Quora’s blockquote formatting. This plagiarism policy applies to people’s own answers on Quora and repeatedly posting the same answer on Quora without blockquotes and attribution is against policy on all answers after April 12, 2016.
Quora doesn’t have a specific policy about Barnum effect (i.e. statements that vacuously apply to anybody); Barnum statements by themselves are not against policy, and would merely fall into the morass of poor answers.
Self-plagiarism is enforced robotically on Quora, and is not uncontroversial: Is Quora’s policy regarding self-plagiarism reasonable?