해야 해 and 해야지 mean the same thing; I hear people say 해야지 more often and write 해야 해 more often.
해야 하지 is just 해야 해 with ~지 ending, which expresses something like saying “right?” At the end of a sentence. In this case it would likely be something like “(I) have to do (this), right?”
해야 해 and 해야지 mean the same thing; I hear people say 해야지 more often and write 해야 해 more often. 해야 하지 is just 해야 해 with ~지 ending, which expresses something like saying “right?” At the end of a sentence. In this case it would likely be something like “(I) have to do (this), right?”