List usb devices:

lsusb

USB devices are listed in:

/dev/bus/usb

the first subdirectory is the bus, the second is the device.

Typical output:

ls -l /dev/bus/usb/003/009
crw-rw-r--+ 1 root root 189, 264 Oct  6 21:09 /dev/bus/usb/003/009