Puppet Debugger is Ruby gem that requires Puppet and Facter to be present. You can use the PDK, Puppet-agent or custom Ruby installation.
When complete, you should be able to run
puppet debugger and see a similar prompt.
$ puppet debugger Ruby Version: 2.4.5 Puppet Version: 5.5.12 Puppet Debugger Version: 0.12.2 Created by: NWOps <email@example.com> Type "commands" for a list of debugger commands or "help" to show the help screen. 1:>>
While Ruby 2.1 will work it is recommended you run a newer, supported version of ruby.
I have a provided some basic instructions for each type of installation in the left column. Use only one of the methods provided.