Is it possible to comprehend happiness if one never experiences unhappiness? In a life in which a person has no negative experiences, is it possible for a person to distinguish especially positive experiences? In other words, can happiness exist without something negative to compare it to?

You ask whether a being that had never experienced unhappiness could experience happiness. Alex appears to be suggesting that happiness requires the possibility of unhappiness. Now that possibility could exist even if it were never actualized. I find no difficulty in imagining a human being who has never suffered a moment's unhappiness living a very happy life. Further, I can imagine a being who is actually incapable of unhappiness being very happy. Many have thought of God in this way.