I travel a lot for work not to my main office. I usually deduct the mileage from my taxes as my employer doesn't reimburse me. Will I be able to deduct the mileage in 2019 under the new tax law?
I think you mean 2018, and the answer is no. For W-2 employees, that type of miscellaneous itemized deduction has been discontinued. On the other hand, the standard deduction has been increased. You may want to discuss your travel arrangements with your employer. Your employer is still allowed to reimburse you for your expenses tax-free as long as you submit proof, such as a mileage log or other records.
If you are self employed, you can still deduct work related miles, the rules have not changed.