I need to put my wireless card into monitor mode and use aircrack-ng tools for wireless pen testing. I tried adding the card to the qube i want to do this with but it says it’s in use by sys-usb.
Can someone help please?
EDIT: this is a debian qube, How do I change the wireless card to my debian qube and why can’t multiple qubes use it simultaneously?
Is the process being done from the tray applet 
or in a different manner?
I’m afraid you might well be stumbling upon this bug right now.
What happens if you remove the external wireless card, reboot the system, then after logging in attach the card to a USB port, and use the aforementioned tray applet to pass it to the Debian-based qube for packet sniffing?
Each qube is an independent virtual computer. You can’t have more than one computer use the same network card at the same time, and it doesn’t matter if they are virtual or not.