To be honest, I'm not sure, but I think it kind of means pointlessness, gratuitousness, and completeness, all together. The adjective I think is almost always used in the phrase "wanton destruction", which is destruction that is pointless, gratuitous, and complete. That's what it means to me anyway.

You will need to give us the word in context, because that's not a "real" English word, but instead a made up slang word.

wantonness n. 1.繁茂，嬉戏 n. 1.繁茂，嬉戏 时　态：wantoned,wantoning,wantons 名　词：wan'tonness 副　词：wan'tonly 同反义词同： [n.] abandon, licentiousness, unconstraint 英英解释 名词解释： the trait of lacking restraint or control; reckless freedom from inhibition or worry she danced with abandon [同] abandon, unconstraint, wantonness the quality of being lewd and lascivious [同] licentiousness, wantonness