If you are at full retirement age, working will not reduce your SS benefit.
If your only income is social security, it's non-taxable. If you have any other income (investments, a job, lottery prize, etc.) then that income is taxable and your social security might also be taxable, depending on how much your other income is, using this formula
https://www.irs.gov/newsroom/dont-forget-social-security-benefits-may-be-taxable
