There are 5 different ways - which one it is?
You did the distro repo way - yes? One of:
sudo apt-get install asciidoctor
sudo yum install asciidoctor
sudo dnf install asciidoctor
You show your $PATH - but not if asciidoctor actually is within the $PATH.
You get something like this?
$ which asciidoctor
/usr/bin/asciidoctor