The correct answer isn't exactly known yet, but, I'm sure there will be no Z-moves in Pokemon: Sword and Sheild. Instead, there will be a feature called "Dynamaxing." I'm not sure what dynamaxing does, but, I do know it will probably be replacing Z-moves. Some people think dynamaxing will also be replacing Mega Evolution, but, I highly doubt it. After all, Z-moves didn't replace Mega Evolution. The only time you can probably see Z-moves in action is when you're battling a foreigner from Alola. But, then again, it wouldn't be fare since you can't use Z-moves. Long story short, Z-moves are most likely not going to be in the game, so, don't get your hopes up.