QuickBooks DNS file is basically categorized into three different file types. They are as follows:

.QBW, is used for all major working files
.QBB, and .QBM, is meant for backup file types
.ND, .DSN, and TLG, is meant for database support files

QuickBooks is no different than any other software, like others it also reads the data file:

QuickBooks: Filename.qbw

The .qbw file extension is usually term as QuickBooks company file , company data file or sometimes as QuickBooks file. It is the principal data file that works as company financial records storehouse. All your data files are saved by QuickBooks.  If you want to find the saved company files and its location:

Start your QuickBooks

Open the company file
Now press on F2 keys
The Product Information page will be displayed to you

In the Product Information Page, you will be able to view all the important information about QuickBooks and the data, including the File Location of your data. If you want to create a backup for the company data, utilize the internal backup function.

Go to File
Click on Back Up/Create Copy.
To know more about qbw file saved on my server but it changes to qbw.dsn

To know more you can check out QuickBooks Error 6190 And 816 troubleshooting