I can't actually tell you where the files are located, but I can tell you what you are looking for.
I've been using Gnucash now for eight or ten years and when I first started it, it asked me where to put the data files. I elected to create a folder called "gnucash_accounts" in my home area and everything is stored in there - except for a few configuration files in ".gnucash" which you have found and which don't contain a file location.
In my "gnucash_accounts" folder I have many accumulated files, one of which is called just "accounts" When I do a new install of gnucash, I just tell it to open that file and all of my data is there.
As well as the plain "accounts" file there are others named as below.
Perhaps a search for files of those names will turn them up for you. Obviously the numeric part being date based won't be the same but the rest should be.
Otherwise, create a transaction and save it and look for files modified at about that time.
Hope that helps.