看看这个。

data = {
    "messages": 
        [
            {"timestamp": "123456789", "timestampIso": "2019-06-26 09:51:00", "agentId": "2001-100001", "skillId": "2001-20000", "agentText": "That customer was great"},
            {"timestamp": "123456789", "timestampIso": "2019-06-26 09:55:00", "agentId": "2001-100001", "skillId": "2001-20001", "agentText": "That customer was stupid\nI hope they don't phone back"},
            {"timestamp": "123456789", "timestampIso": "2019-06-26 09:57:00", "agentId": "2001-100001", "skillId": "2001-20002", "agentText": "Line number 3"},
            {"timestamp": "123456789", "timestampIso": "2019-06-26 09:59:00", "agentId": "2001-100001", "skillId": "2001-20003", "agentText": ""}
        ]
}

var = []

for row in data['messages']:
    new_row = row['agentText'].split()
    if new_row:
        var.append(new_row)

temp = dict()

for e in var:
    for j in e:
        if j in temp:
            temp[j] = temp[j] + 1
        else:
            temp[j] = 1

for key, value in temp.items():
    print(f'{key}: {value}')