how to run local command via ansible-playbook

I like delegate_to. Here's an example that, on localhost, runs getent hosts for each host:

---
- hosts: all
  connection: ssh
  gather_facts: true
  tasks:
  - name: Lookup ansible_hostname in getent database
    command: getent hosts {{ ansible_hostname }}
    delegate_to: localhost
    register: result

  - name: Show results
    debug:
      var: result.stdout
    delegate_to: localhost

You could access the hostname by using the following play, as the inventory information are available as hostvars.

- hosts: 127.0.0.1   
  connection: local
  gather_facts: no

  tasks:
    - debug: var=hostvars

    - name: node create
      command: "knife node create {{ hostvars[item]['hostname'] }}"
      with_items:
        - "{{ groups['qa-hosts'] }}"

Another alternative is local_action.

In the case of both delegate_to and local_action, be aware that if become = yes then Ansible will of course implicitly try to invoke the action using sudo, and then will probably fail because the password for local sudo will be different to any password you entered for remote sudo.