I don't understand Form 4562 (Schedule C) and the question regarding supporting evidence.

[KarenL2]

It sounds like it's asking about your vehicle deduction.  When the question about "evidence" is asked, the IRS needs to know that you have written documentation of your vehicle business-use mileage.  It is required to keep a log of mileage in order to take the vehicle expenses.  You would include the date, the business purpose, where you went/who you met, and the total miles.