I am using a powerpc, and after building and flashing the linux kernel on the device I can see the file system. But if I try to create a user or make any changes they get erased and resets to default after I reboot the device. The kernel image location is on network. I am not able to save my changes.

I am using kernel parameter as root=/dev/ram0 I have also used root=/dev/nfs nfsroot=|ip, rootdir| but it is not getting mounted

How can I see the file system of my target on my host linux such that , I can see the target device kernel file system on my host machine and save if even I reboot the device.

In my experience, I've seen a deeply embedded system, where the actual running target RFS(Root file system) was actually decompressed from an archive (.tar) into ram on boot. If this is what you have, you will need to edit the file system inside that generated archive to change the running target system RFS.

You might have better success by going to an embedded Linux forum than us. I suspect most of us are RTOS/bare iron folks - not that we are against Linux, we just have a different focus. (Some of us have experience with embedded Linux, like Jim_255 and myself, but I suspect most of us are not at the down & dirty level to give you specific advice. I know I am not, and I have used embedded Linux in a number of projects, but I was not the one who did the port.)

When you find the answer, please let us know!

As Jim said, probably you are decompressing your file system at boot time. But you should provide more info about your system, like boot parameters. 

I suppose root=/dev/ram0 is not what you want.

Ex. Save your file system on flash and boot from there root=/dev/mmcblk0p2 rw rootfstype=ext4