The following command retrieves the access control list for a bucket named my-bucket:

aws s3api get-bucket-acl --bucket my-bucket

Output:

{
    "Owner": {
        "DisplayName": "my-username",
        "ID": "7009a8971cd538e11f6b6606438875e7c86c5b672f46db45460ddcd087d36c32"
    },
    "Grants": [
        {
            "Grantee": {
                "DisplayName": "my-username",
                "ID": "7009a8971cd538e11f6b6606438875e7c86c5b672f46db45460ddcd087d36c32"
            },
            "Permission": "FULL_CONTROL"
        }
    ]
}