If you are moving to a new console or want a safety backup, you have several options:
Use the Save Data Transfer Tool from the Nintendo eShop to move data from a physical card to a digital version. project x zone 2 save file
If your 3DS has custom firmware, apps like Checkpoint allow you to export decrypted save files to your SD card. These files are typically found in /3ds/Checkpoint/saves/[Game Name]/ . If you are moving to a new console