A law office has a judgment on me that they haven't enforced yet. They send me a form every six months called a personal financial statement. Asking for my name address, gross and net income, expenses, assets and last but not least, pay stubs and tax returns to verify my income.
Now that the creditor has a judgment against you, it is entitled to question you about property, income etc. You must answer these questions truthfully. In some states, you can be asked to appear in court to answer similar questions.
I can't say for certainty whether you are required to provide your tax returns. You would really have to ask an attorney in your area that question. Keep in mind that creditors/collectors with a judgment against you typically have greater avenues for collection than a creditor or collector who hasn't sued you.
If you haven't done so already, you may want to set up a free consult with a bankruptcy attorney who can explain your rights and options for dealing with this debt.