If you've answered all the questions in a way that Turbo Tax will apply the deduction (Exclusive Use, Required by Employer, Used to Meet Clients - if applicable), and you're still not seeing the deduction applied, it may be because the amount of the deduction is not enough to surpass the Standard Deduction.
Home Office and other Self Employment expenses require that you itemize your return. Turbo Tax will automatically determine if you should use the Standard Deduction (6,300 for singles and married persons filing separate returns and $12,600 married filing jointly), or Itemized Deductions, based upon which is greater in order to guarantee you the largest return. If you just want to get confirmation that Turbo Tax is working properly, you could enter a home office deduction that is greater than your Standard Deduction and see if it changes your return...just don't forget to put it back.
Disclaimer: I do NOT work for Turbo Tax and I would never advise, suggest, or imply that a taxpayer submit invalid data on a return.