How to open .cfg file on iOS
A .cfg is a config file for programs, saved in plain text, used in Windows.



To view on iOS simply...


Install iFile 
Transfer the file to your iOS Device (Easiest is via iCloud)
Open iFile
Import into iFile (For iCloud: Navigate to Clouds>iCloud>Select File)


6.Go to Files 

7.Tap on the file to view





To edit (and/or view) simply...


Rename file.cfg to file.cfg.txt
Transfer the file to your iOS Device (Easiest is via iCloud)
Install Textor
Open the file in Textor and edit






Note: I am not affiliated with any of the apps above and will not gain financially or otherwise from the purchasing/downloading/using of these apps. They were merely suggestions.