I use software in Unix, I am trying to edit the file before final printing. Because the software only let me enter the data into, then print out, during printing, unix will save file buffer in some where to be ready print, if now I cancel the printing job, the file's buffer should be in spool, and then can I edit this buffer, and continue to print?

/var/spool is one common place.
But the file may not be there - once you cancel the print job the file is marked for deletion.

Does the software not have some kind of 'I want a copy of the file' option?

which command to check printing list and find out what job is ready to print in queue. So when I cancel the printing job, meantime, the file buffer is also be canceled, right? Best way is I save the file under the Unix, and then edit the file, finally print out through unix command, right?

Yes, that is what I would suggest.