Q:

How to open or mount unopenable or unmountable ISO

I downloaded two .iso files, but couldn't open them with Ark. So I installed 7zip using wine (software called wine, not actual alcohol) and was able to open and extract one of them, but I'm still unable to open or extract other one.  
Also, assuming the iso files are damaged, is there way (or software) to open them? 
Any suggestions?      
Note: I use Kubuntu.  
Edit:
Using:
sudo -i
mount -o loop /home/ftl/Downloads/folder/file.iso /mnt  

results in:
   mount: wrong fs type, bad option, bad superblock on /dev/loop0,
   missing codepage or helper program, or other error
   In some cases useful info is found in syslog - try
   dmesg | tail or so. 

A:

Sounds as if the iso are corrupt.  Otherwise you can loop mount them. 
sudo -i
mount -o loop your.iso /mnt

The files are then available under /mnt.  Post any error messages you get. 
If you want a graphical interface use gisomount
See https://help.ubuntu.com/community/MountIso for additional information.