Hi,
For the install method based on the tar,gz file, you don't need GPG to make KrakenD work. This is for Debian-based, and CentoOS/Redhat based distros, not your case with Oracle Linux.
After decompressing the targz, you can see in the screenshot you have shared, that it creates a folder /home/oracle/usr/bin with the binary "krakend" inside (and other files). You can simply move the binary to any directory that is included in your PATH (find it out by typing "echo $PATH"). For instance, you can do:
mv /home/oracle/usr/bin/krakend /usr/local/bin/krakend
Then the krakend command will work.
Hope this helps move forward