After talking to a TurboTax support person, after posting my question, I concluded that entering zero personal use days was NOT correct. I considered that personal use consisted of the days that I used the office space vs. the days that the sublessee used the office space. In my situation, the sublease was for only part of 2017. On Schedule E, Pt 1, Line 2, I entered 15 days "Fair Rental Days" and 55 days "Personal Use Days". Note that I concluded that line 2 is really meant for residential sublease, not Commercial (Type 4 property).
Yes, the rent paid to the owner is put onto schedule C. The sublessee rent goes onto schedule E.
Hope this helps!!
