Visitor and Session Numbers from QRcode

Visitor and Session nummber from QR code on our campaign materials,
to which Category is it reflect on ? Social??

Assuming the only 4 channels you have are the ones in your screenshot, QR code traffic is being assigned to the Direct entry channel.

You need to add tracking parameters (UTM or PK) to your links when you generate your QR codes, only then the traffic they generate will be added to the Campaign channel.

See more information about default channels.