You cannot report withholding without documentation. Anyone that withholds tax and sends that tax to the government is required by law to report it with your SSN and provide you with the documentation. It is possible that the organization did not know the law or was a scam to collect and pocket withholding.
Also the maximum backup withholding on pools is 24%.
If you mean "pool" as the game of pool that you compete in, then I believe that is a game of skill and not gambling, if you are the competitor. If over $600 then you should have received a 1099-MISC. You can report the income as miscellaneous income but you still need documentation to claim any withholding since withholding must be sent to the IRS and applied to your account which cannot be done without your SSN.
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
