Create Bootable USB Stick from Bundle (Terminal)

Dear Friends

I want to create a bootable usb stick with AHT for my Mac Mini 6,1 . The problem is that the .DMG is bundle and the standard terminal code doesn't work:

cp -r /Volumes/AHT/System /Volumes/USBstick/
sudo bless --folder /Volumes/USBstick/ --file /Volumes/USBstick/System/Library/CoreServices/.diagnostics/diags.efi --label AHT

Can you please help me find what to type for the bundle .dmg so I can boot succesfully to AHT from a USB Stick?

Sincerely
coa00kt