Where do you include deductions for professional conference expenses?

As an employee, you get no federal income tax deduction.  Some states allow a deduction. Entry would be done on federal schedule A in the section for job-related expenses. 

Unreimbursed employee expenses were once deductible for W-2 employees, but the Tax Cuts and Jobs Act of 2017 suspended the deductions for most workers from 2018 to 2025. Certain workers can file Form 2106 to calculate deductible unreimbursed expenses.  Review the TurboTax article Are Unreimbursed Employee Expenses Deductible? for more information.

If you are a worker who meets the exception or your state allows you to deduct unreimbursed employee business expenses, review the TurboTax article Where do I enter job-related employee expenses? (Form 2106) for navigation instructions.