The register parameter can be used to store the JSON output of a task in a variable. In this example, the JSON output of the shell task will be stored in a variable named "out". Often, the debug module is then used to display the content of the variable.

---
- hosts: localhost
  tasks:
  - shell: ps
    register: out

  - debug:
      var: out
...

Which should output something like this.

TASK [shell] 
changed: [localhost]

TASK [debug] 
ok: [localhost] => {
    "out": {
        "changed": true, 
        "cmd": "ps", 
        "delta": "0:00:00.075407", 
        "end": "2022-09-29 03:06:03.478331", 
        "failed": false, 
        "rc": 0, 
        "start": "2022-09-29 03:06:03.402924", 
        "stderr": "", 
        "stderr_lines": [], 
        "stdout": "   PID TTY          TIME CMD\n 39957 pts/0    00:00:01 ansible-playboo\n 40165 pts/0    00:00:00 ansible-playboo\n 40238 pts/0    00:00:00 sh\n 40242 pts/0    00:00:00 python2\n 40253 pts/0    00:00:00 ps\n112376 pts/0    00:00:00 bash", 
        "stdout_lines": [
            "   PID TTY          TIME CMD", 
            " 39957 pts/0    00:00:01 ansible-playboo", 
            " 40165 pts/0    00:00:00 ansible-playboo", 
            " 40238 pts/0    00:00:00 sh", 
            " 40242 pts/0    00:00:00 python2", 
            " 40253 pts/0    00:00:00 ps", 
            "112376 pts/0    00:00:00 bash"
        ]
    }
}

You can also output just the value of a specific key, such as the stdout_lines key (in this example).

---
- hosts: localhost
  tasks:
  - shell: ps
    register: out

  - debug:
      var: out.stdout_lines
...

Which should output something like this.

ok: [localhost] => {
    "out.stdout_lines": [
        "   PID TTY          TIME CMD", 
        " 44334 pts/0    00:00:01 ansible-playboo", 
        " 44904 pts/0    00:00:00 ansible-playboo", 
        " 44926 pts/0    00:00:00 sh", 
        " 44929 pts/0    00:00:00 python2", 
        " 44946 pts/0    00:00:00 ps", 
        "112376 pts/0    00:00:00 bash"
    ]
}