I was just wondering if Citra supports QR scanning, and if yes, how? I’d love to use it for my Pokemon Sun game.
In order for us to provide better support, we need to see the log generated by Citra. This guide will walk you through how you can obtain the log file: How to Upload the Log File.
We support qr scanning, you link the qr image as a static file to the camera you would scan with ingame (front or back as needed) Depending on the size of the qr image, you might have to edit it to either expand or shrink it, so it fits appropriately.
Where exactly do I put the image I need in?
Configure -> system -> camera -> still image, then feed it whatever picture you have, editing as necessary to have it fit appropriately.
Okay, thank you! 
Sorry to bother, I got the part where I need to put the image in, but do I select (Camera to Configue) Rear or Front? Do you also maybe know what format do I need to fit in the image?
you use whatever camera the 3ds would point at the image. Usually this is rear, I think?