how to set tap face to speak time

Make sure that Silent mode on your Watch is turned off.

On the watch go to; Settings>Sounds & Haptics>Silent Mode

Tap and hold the screen with two fingers.

ASC - Late 2012 Mac mini, macOS 10.14.6; Watch, series 5 GPS/cellular, watchOS 6.2.8; iPad Air 2, ipadOS 13.6.1; iPhone 8+, iOS 13.6.1; TV 4th Gen, tvOS 13.4.8;  HomePods, audioOS 13.4.8 and Airport Express w/ Airplay 2