The following command lists all of the parts that have been uploaded for a multipart upload with key multipart/01 in the bucket my-bucket:

aws s3api list-parts --bucket my-bucket --key 'multipart/01' --upload-id dfRtDYU0WWCCcH43C3WFbkRONycyCpTJJvxu2i5GYkZljF.Yxwh6XG7WfS2vC4to6HiV6Yjlx.cph0gtNBtJ8P3URCSbB7rjxI5iEwVDmgaXZOGgkk5nVTW16HOQ5l0R

Output:

{
    "Owner": {
        "DisplayName": "aws-account-name",
        "ID": "100719349fc3b6dcd7c820a124bf7aecd408092c3d7b51b38494939801fc248b"
    },
    "Initiator": {
        "DisplayName": "username",
        "ID": "arn:aws:iam::0123456789012:user/username"
    },
    "Parts": [
        {
            "LastModified": "2015-06-02T18:07:35.000Z",
            "PartNumber": 1,
            "ETag": "\"e868e0f4719e394144ef36531ee6824c\"",
            "Size": 5242880
        },
        {
            "LastModified": "2015-06-02T18:07:42.000Z",
            "PartNumber": 2,
            "ETag": "\"6bb2b12753d66fe86da4998aa33fffb0\"",
            "Size": 5242880
        },
        {
            "LastModified": "2015-06-02T18:07:47.000Z",
            "PartNumber": 3,
            "ETag": "\"d0a0112e841abec9c9ec83406f0159c8\"",
            "Size": 5242880
        }
    ],
    "StorageClass": "STANDARD"
}