A stylus designed specifically for an iPad, like the Apple Pencil or a third-party option like a Zagg Pro Stylus, will be made with a soft tip and therefore will be unlikely to run any risk of damaging an iPad. The only real danger will be if you use a stylus that isn't intended for an iPad, and hasn't been optimised specifically for an iPad screen. It may damage the iPad screen, and also probably won't work all that well. So stick with an iPad-specific stylus and you shouldn't run into any problems.