The same applies for Docker and for a container. Each container has its own file system structure in accordance to the link above.
In your screen shot I see a drive letter "D:\". This is windows and not Linux. In Linux everything starts with "/" as root folder followed by the folder you want to put your data in.
If you want to look into container then you can use Docker Web-GUI calling an embedded console clicking this icon followed by clicking "connect":
In this container console you can use the Linux command "dir" to list the container's folder structure
And the you can choose the folder you like. I would use the "/var/myfile.csv" folder.
P.S: wery important is that netPI SD card has a lifetime of 10TByte written overall. So if customer wants to write millions of data into CSV database the SD card is getting weared and get destroyed. Read in forum about the chapter SD card durability to get more details
„You never fail until you stop trying.“, Albert Einstein (1879 - 1955)