Investors are on edge for Jerome Powell's Jackson Hole speech. What to watch for, and what could go wrong.

Federal Reserve Board Chair Jerome Powell testifies before the Senate Committee on Banking, Housing, and Urban Affairs on 'The Semiannual Monetary Policy Report to the Congress', at Capitol Hill in Washington on Tuesday, July 17, 2018.

Jose Luis Magana/AP

• Investors await Jerome Powell's Jackson Hole speech amid volatile markets and economic data.
• July's weak economic data and high unemployment have heightened the focus on jobs and inflation.
• Global central bank coordination...