There are a few ways that you can try to capture snaps on Snapchat without knowing them. Everyone knows that Snapchat sends notifications to users if someone takes a screenshot of their snaps.
If you think about it, it is possible to take screenshots on Snapchat without their knowledge. Well, it is possible, and the only way to do it is to use a spare phone to capture the snaps of someone without knowing them. Take another phone and start the camera on it. Then you have to open Snapchat on your phone and capture the snaps through the camera on another phone.
Turn Airplane Mode on, turn Wifi off, open the Snap, and screenshot. Turn Airplane Mode on, keep Wifi on, open the Snap, and screenshot. Open the Snap, then turn Airplane Mode on. Close Snapchat, turn Airplane Mode on, then re-open the app and screenshot.