The product key should come with your licence of Dynamo Studio, have a look where the Serial Number is on Autodesk Accounts or any correspondence you have received from Autodesk. It should come with it but unfortunately I cannot find this online to provide you.
I guess you could try 535I1 from here...
https://cadblognews.com/2016/04/04/autodesk-2017-product-keys-2/