data = { "results": [
    {
        "event_id": "1234",
        "event_date": "2019-05-01",
        "event_date_slot": "1"
    },
    {
        "event_id": "1235",
        "event_date": "2019-05-01",
        "event_date_slot": "2"
    },
    {
        "event_id": "1236",
        "event_date": "2019-05-02",
        "event_date_slot": "1"
    },
    {
        "event_id": "1237",
        "event_date": "2019-05-02",
        "event_date_slot": "2"
    }
  ]
}
print("ID|Date|Slot 1|Slot 2")
for r in data['results']:
    print("{}|{}|{}|{}".format(r['event_id'],r['event_date'],r['event_date_slot'],r['event_date_slot']))

ID  |Date      |Slot 1|Slot 2
1234|2019-05-01|1     |1
1235|2019-05-01|2     |2
1236|2019-05-02|1     |1
1237|2019-05-02|2     |2

Date      |Slot 1|Slot 2
2019-05-01|1234  |1235
2019-05-02|1236  |1237