For WiFi/Cloud cameras;
The QR code is printed on the label placed on the device. You can also find the QR code on the Quick start guide that comes with the device.
For EZVIZ DVRs/NVRs:
The QR code can be found in the system management menu.
Connect the DVR/NVR to a monitor using a HDMI cable
Input your device password
Go to the system information menu > The QR code will be located there