You'll have to check with each agency individually.  Most of them mail out a tax form in January, at least in the U.S. - not sure about other countries.  If not, they usually have a tax center on their web site where you and view or request a copy for tax purposes.  DT doesn't seem very good about this and doesn't mail anything out unless you are over a certain amount.  If you haven't received anything, I would go to each site and look for their tax page, then send them a message if necessary.  The backup plan (for me at least) is to use Paypal receipts - provides a summary of what was paid out.  Good luck!