Can't Scan Alexa Provided DynamoDB Table

DynamoDB does not use resource based access control, therefore, you will have to add the necessary permissions to your user role arn:aws:sts::952997128153:assumed-role/AlexaHostedSkillLambdaRole. Adding something like the following:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "MyPolicy",
            "Effect": "Allow",
            "Action": [
                "dynamodb:Scan"
            ],
            "Resource": "arn:aws:dynamodb:us-east-1:952997128153:table/<YourTableName>"
        }
    ]
}

If you do not have permission to add policy to an IAM role, then you should reach out to your accounts admin to do so.

Further info: https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/using-identity-based-policies.html