I use my car for daily business. I junked one in 2017 for $100. They are asking that since I didnt claim depreciation they need the total cost? How can I reflect this?

If you took actual expenses on that car, they want the cost of the car when you first put it in service.  Then even though you didn't depreciate the car, they will subtract what depreciation should have been taken on it to see if you have any value left to take off the junk value of $100.