Run the below command in the terminal to see the contents of a tar.gz file without extracting it:

tar -tf filename.tar.gz

-t, --list

List the contents of an archive. Arguments are optional. When given, they specify the names of the members to list.

-f, --file=ARCHIVE Use archive file or device ARCHIVE...

It's probably a GNU specific option, but you could use the -O or --to-stdout to extract files to standard output

$ tar -axf file.tgz foo/bar -O