To view a file with the .gz extension it needs to be uncompressed, or unpacked.
Examples of gzip composed files are the log files found in the directory /var/log. In this directory the older log files are stored compressed. To show this they have the .gz extension
For example the syslog files are:
syslog syslog.1 syslog.2.gz syslog.3.gz syslog.4.gz
The gz file extension is used to signify that the file had been compressed using gzip.
To decompress a gzip file there are a number of programs available, including gunzip and gzip.
Either may be used as a simple command with the file name to uncompress the file.
gunzip
gunzip syslog.2.gz cat syslog.2.gz
gzip
gzip -d syslog.2.gz cat syslog.2
