I think they do have a copyright, but since reaction vids can often help more people to get to know SKZ better, so it seems JYP Entertainment won't block the reaction vids in KZfaq (since I saw many). But even though it's SKZ contents if it was made by other production teams such as some TV stations or some independent KZfaq channels other than JYP Entertainment, some of them are allowed and some are not, depending on those production teams' own policies So the reaction clips for MV or other contents in JYP Entertainment or official SKZ Channels are okay, I think (but not sure for those at SKZ Japan official Channel)😊