Can i take union dues paid to employer as deduction for NY state taxes on line line 21 form it-196

You will need to enter the union dues in the federal software so that they flow to the state return.

W-2 employees cannot deduct job-related expenses on a federal return.  Job-related expenses were eliminated as a federal deduction for W-2 employees by the tax laws that changed for 2018 and beyond.  Your state tax laws might be different in AL, AR, CA, HI, MN, NY or PA.

If you live in a state that lets you deduct job-related expenses, the information will flow from your federal return  to the state return, so enter it in Federal>Deductions and Credits>Employment Expenses>Job-Related Expenses

Yes.  If you are itemizing the amount of union dues paid that exceed the employer reimbursement amount are deductible as an "Unreimbursed Employee Business Expense" on NY form It-196.