Looking at my 2015 turbotax documents where can I find the square footage I entered for my home office per an IRS request/audit?

If you used a home office as a self-employed person the form is Form 8829 Part I, line 1.

If you used a home office as an employee, the worksheet is called Employee Home Office worksheet, Part II line 1.This is a TurboTax worksheet and not an IRS form.