Where can I find the sales tax paid on a vehicle I purchased in 2017?

I would recommend you to check your receipt of the payment including personal checks and credit card statements.  If you purchased from a dealership, you might be able to contact them to obtain the information from their record.  You might not have paid any sales tax if you live in one of the five states below. 

Here is some additional information for your reference:

Whether you're buying a new car or a used car, or even leasing a car, you'll have to pay state sales tax. Nearly every state has a sales tax, ranging from under 3 percent to over 8 percent. 

There are currently five states that do not have a sales tax: Alaska, Delaware, Montana, New Hampshire, and Oregon. Municipalities within these states can still levy taxes.  Check locally to see if any sales taxes apply to your new car purchase.

I am about to contact CA DMV to try to get a receipt from my initial registration when the Use Tax would have been collected.

The title form shows "Fees Paid" which is a combination of the Use Tax and registration fees but it is not broken out and doesn't identify the tax specifically.

If I can prove I paid use tax already, Im going to have to pay it again to another state.  

I'm having this exact same issue with California- title says "Fees paid" but WA state is saying they can't assume that includes sales tax.

Did you get this figured out? 

Did you ever find anything out from CA DMV