The IRS says: 

Many owners of sole proprietorships, partnerships, S corporations and some trusts and estates may be eligible for a qualified business income (QBI) deduction – also called Section 199A – for tax years beginning after December 31, 2017. 

Since no way to calculate or report the 199a deduction on Form 1120, there is no place to enter box 20z. 

https://www.irs.gov/newsroom/qualified-business-income-deduction