Is it possible to save a csv file of trace A and read it via GPIB command with Yokogawa AQ6370C ?
If yes, what's the procedure ?
The procedure to transfer a trace is going to be documented in the manual. You might also want to check with Yokogawa to see if they have an instrument driver for whatever programming language you are using.
If you are using LabVIEW you can find several save VI's from the Yokogawa driver lib.
You can also have a look at the AQ6370 Viewer from Yokogawa. (get the data through a TCP/IP connection)