There are a few ways you can take screenshots on Snapchat without them knowing on your iPhone. One of the popular ways is to take a screenshot after you screen-share on a different device. Another method involves taking a screenshot from the multiple apps screen where you multi-task from. You can also try out this method: 1. Open Snapchat on your iOS device. 2. Turn on airplane mode. 3. Right after, you have to take a screenshot. 4. Immediately, restart your device. 5. Turn off airplane mode. This lets you take screenshots on Snapchat without them knowing on iOS.