cust.yml

- hosts: localhost
  gather_facts: no
  connection: local
  vars:
      customer:
        - name: cust1
          events:
          - name: event 1
            letter: birthday
          - name: event 2
            letter: holiday
        - name: cust2
          events:
          - name: event 1
            letter: child 1
  tasks:
    - debug: var=customer

    - debug: var=item
      with_subelements:
         - "{{ customer }}"
         - events

    - debug: msg='/customer/{{ item[0]["name"] }}/letter/{{ item[1]["letter"] }}'
      with_subelements:
         - "{{ customer }}"
         - events

gistfile1.txt

PLAY [localhost] ***************************************************************

TASK [debug] *******************************************************************
ok: [localhost] => {
    "customer": [
        {
            "events": [
                {
                    "letter": "birthday",
                    "name": "event 1"
                },
                {
                    "letter": "holiday",
                    "name": "event 2"
                }
            ],
            "name": "cust1"
        },
        {
            "events": [
                {
                    "letter": "child 1",
                    "name": "event 1"
                }
            ],
            "name": "cust2"
        }
    ]
}

TASK [debug] *******************************************************************
ok: [localhost] => (item=[{'name': 'cust1'}, {'name': 'event 1', 'letter': 'birthday'}]) => {
    "ansible_loop_var": "item",
    "item": [
        {
            "name": "cust1"
        },
        {
            "letter": "birthday",
            "name": "event 1"
        }
    ]
}
ok: [localhost] => (item=[{'name': 'cust1'}, {'name': 'event 2', 'letter': 'holiday'}]) => {
    "ansible_loop_var": "item",
    "item": [
        {
            "name": "cust1"
        },
        {
            "letter": "holiday",
            "name": "event 2"
        }
    ]
}
ok: [localhost] => (item=[{'name': 'cust2'}, {'name': 'event 1', 'letter': 'child 1'}]) => {
    "ansible_loop_var": "item",
    "item": [
        {
            "name": "cust2"
        },
        {
            "letter": "child 1",
            "name": "event 1"
        }
    ]
}

TASK [debug] *******************************************************************
ok: [localhost] => (item=[{'name': 'cust1'}, {'name': 'event 1', 'letter': 'birthday'}]) => {
    "msg": "/customer/cust1/letter/birthday"
}
ok: [localhost] => (item=[{'name': 'cust1'}, {'name': 'event 2', 'letter': 'holiday'}]) => {
    "msg": "/customer/cust1/letter/holiday"
}
ok: [localhost] => (item=[{'name': 'cust2'}, {'name': 'event 1', 'letter': 'child 1'}]) => {
    "msg": "/customer/cust2/letter/child 1"
}

PLAY RECAP *********************************************************************
localhost                  : ok=3    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0