I'm trying to find where to enter the business use of my car?

Sorry----claiming mileage as a federal deduction for driving from one W-2 job to another job was eliminated when the tax laws changed for 2018 and beyond.

https://ttlc.intuit.com/questions/4482873-which-federal-tax-deductions-have-been-suspended-by-tax-reform

Assuming your 2nd job is also a W2 job, then as Xmasbaby0 states that is no longer a federal deduction unless you are in one of the categories below.  You may however be able to get a deduction on your state returns.  The amounts entered will automatically transfer to your state return if applicable. 

In the Deductions and Credits section scroll down to "Employment Expenses" and "Start/Revisit" the "Job expenses for W2 income" topic. 

- Armed Forces reservist
- Qualified performing artist
- Fee-basis state or local government official
- You're disabled and have impairment-related expenses