这应该有效:

b = [{'internal': False, 'protocol_parameters': [{'name': 'identifier', 'id': 1, 'value': 'x.x.x.x'}]},
{'internal': False, 'protocol_parameters': [{'name': 'identifier', 'id': 0, 'value': 'y.y.y.y'}, {'name': 'incomingPayloadEncoding', 'id': 1, 'value': 'UTF-8'}]},
{'internal': False, 'protocol_parameters': [{'name': 'incomingPayloadEncoding', 'id': 1, 'value': 'UTF-8'}, {'name': 'identifier', 'id': 0, 'value': 'z.z.z.z'}]}]

for a in b:
     c = next(param.get('value') for param in a['protocol_parameters'] if param.get('name')=="identifier")
     print(c)