Is a usb client with the fez panda 1 possible without a shield.
There is no difference between panda 1 and 2 regarding the USB port; it can be either configured as a client OR host usb port.
The USB port on the panda actually is a USB client port.
You can choose to transform it into a USB host port (but not both at the same time, for that you would need a Fez domino):
So if I want to develop a program that use the fez as a usb client but for debugging I can use this
Yes, or any other USB to serial TTL cable !
Just connect the MOD pin to GND (which will tell the panda to use serial debugging instead of USB)
Use it with eblock shield and it will be all a peice of cake