Have done quite a bit of work with the network based Prologix, needed to get some of the lab instruments on the network. You need to set up the prologix adapter first, with it's own gpib address, and also, the gpib address of the remote instrument. The usb adapter looks like it has the same command set as the network version, so first make sure you can talk to the adapter. The ++help command should return a page full of text, so it's a good way to verify the comms path pc -> usb -> prologix, first. Once that's done, you should be able to send an instrument command that returns something in text, and you should be good to go.
Just recently uploaded a project to sourceforge. Early days, and doc is a bit light at the mo, but its a complete stack that uses shell script at top level and abstracts the prologix and lower layers to simplify usage at the top. Versions for FreeBSD and Linux and even builds and runs on cygwin / windows. You can find the prologix init code in the functions.sh file. Present version is for the lan adapter, but it's modular, so should be able to modify for usb or other interface. No connection with the company btw, just something I needed for work. Find it here:
https://sourceforge.net/projects/network-instrument-workbench