Here is a quick guide on how to screenshot on Snapchat without them knowing, it's so easy and simple.
Step 1: It is important that you know how to take a screenshot on your iPhone or iPad. Here are two ways you can do it:
Press the Sleep/Wake button at the same time as the home button on your device (or just press the Sleep/Wake button if you don't have a home button).
Use AssistiveTouch to take screenshots. To do this, go to Settings > General > Accessibility > AssistiveTouch, then turn on AssistiveTouch and enable Screenshot.
Step 2: Open Snapchat and find the picture or video message you wish to take a screenshot of. If it is a picture, tap it once to open it and then tap again in order to expand it into full screen mode. If it is a video message, tap once in order to play it back before pressing again in order to expand into full screen mode.
Step 3: Once your image or video has expanded into full screen mode, simply press down on the screen with two fingers and hold for about one second before letting go of one finger while still holding down
Read More: https://www.guidebrain.com/fix-snapchat-keeps-crashing-on-android-iphone/
if you had issue with screenshot on Snapchat then I suggest you to download and this WhatsApp plus at https://gbapps.net/ it's officials website...