What is a Linux ISO?

Downloadable binary file containing a CD/DVD disc image of a Linux distribution

Given the text "fileone,filetwo,filethree,filefour", you need to delete all of the .sh files with those names (fileone.sh filetwo.sh…), how can you do it with brace expansion?

In order to use brace expansion, you need to add it to take the list and use it in braces - rm -f {fileone,filetwo,filethree,filefour}.sh.

You have a scripts directory called /scripts/ and you want to add it temporarily to your executable path, how can you do that?

Your executable path are extracted from the environment $PATH, you can add temporary item to it on the current shell using - export PATH=$PATH:/scripts.

If I have configured the parameter TTL in my domain configuration file (named) to 14400, what does it mean?

The domain TTL configuration is setting the time which name-servers querying the name server will cache the results in their DB before asking the server for new configuration.
14400 seconds is 4 hours.

You want to encrypt and password-protect a password file "mysecret.txt", how can you do it with GPG and then decrypt it to view the contents?

In order to gpg encrypt a file, you type "gpg -c mysecret.txt" and choose your desired password.
In order to decrypt it and view the contents, you type "gpg -d mysecret.txt.gpg"