If I report my 2018 rental income and expense on Schedule E, will I be able to deduct 20 per cent of the net rental income as a Trade or Business on page 2 of the 1040?

Yes but the mechanics of this quasi 20% deduction is still unclear and until some regs come out all we can do is speculate ... I look forward to seeing how this messy code section will be explained and the forms/worksheets it will produce. 

https://www.forbes.com/sites/anthonynitti/2017/12/26/tax-geek-tuesday-making-sense-of-the-new-20-qualified-business-income-deduction/#7145e5244fda

It is still unclear if rental property qualifies as a "Trade or Business" for the 20% reduction that was enacted by the new law.

Hopefully the IRS will clarify within the next few months.

However, many people, including Continuing Education Providers for tax professionals, have been asserting that rentals do qualify.  But again, we will need to wait for the IRS to clarify the matter.