Where does an employee salesperson enter business mileage for use of personal vehicle? Does this go in self-employment area?

If you are a W-2 wage employee then none of your employee business expenses are deductible on a federal tax return due to the tax code changes in effect for tax years 2018 thru 2025.

No. Unfortunately miscellaneous itemized deductions are suspended.

The previous deduction for job-related expenses or other miscellaneous itemized deductions that exceeded 2 percent of your adjusted gross income is suspended.

This includes unreimbursed employee expenses such as uniforms, union dues and the deduction for business-related meals, entertainment and travel, as well as any deductions you may have previously been able to claim for tax preparation fees and investment expenses, including investment management fees, safe deposit box fees and investment expenses from pass-through entities.