What is the tax deduction percentage for professional organization dues?

If you are taking the deduction on your schedule A you would list the full value of the dues. However it would be a miscellaneous deduction subject to a 2% limitation. If you have a Schedule C you can take the full amount of the dues without any limitation.

You can deduct all of it, not just a percentage - BUT - if you are an employee, to do so you have to itemize, and you can only deduct the amount of unreimbursed employee business expenses that exceeds 2% of your income

If you have your own business, then it would be an expense on your schedule C.

Remember this is a deduction, not a credit. Your actual tax savings for a deduction is the amount of the deduction times your marginal tax bracket.

If you are self-employed, you can deduct it as a business expense on Schedule C. If you are an employee, you can include the amount in Miscellaneous deductions on Schedule A, subject to the 2% limitation.