Depending JSON file structure and which level you would like to iterate through, it will be different.
If the JSON file is a list of entries, and each entry is a dict like this {“serial_number”:"…",“timestamp”:…,“data”:[…]}, then:
dictionaries = json.load(f)
for row in dictionaries:
    data = row['data']

If the JSON file is dict with keys such as “serial_number”, “timestamp”, “data” (i.e. {“serial_number”:"…",“timestamp”:…,“data”:[…]}) , then:
d = json.load(f)
serial_number = d['serial_number']
timestamp = d['timestamp']
data = d['data']
for point in data:
    # You can iterate through the data here, or you can just convert it to a Tensor