It's a difficult sentence, and the context isn't clear, but I shall try. "굴지의 기업 총수라고 해서" = as a leading company CEO (or something like, "it being the case that he is a leading company CEO") "특별히 더 행복해 보이지 않는 것만 보더라도" = just seeing that he doesn't appear to be especially more happy "그 사실을 잘 알 수 있다" = you can know what is involved (or the truth that is involved) So observing that he doesn't seem particularly happy, even though he is a prominent company CEO, something must be wrong.

Simply, it means, 특별히 더 행복하지 않다. "특별히 더 행복해보이지 않는 것만보더라도", Here, "....만 보더라도" = 다른것(증거)도 있는데 이것만으로도. We do have more other evidences, but only from this fact(굴지의 기업총수인데 특별히 더 행복해보이지 않는것).. bla-bla-bla He doesn't looks more happier than somebody else because he is (xxxxx), From this fact, we can understood (realized) that (xxxx something truth? ) A verbose representation....