Can I listen to Bumps after the workout is over?

Yes, you can listen to Bumps by scrolling down on the Workout Summary screen (see pic 1 below) or on the Workout History screen.  To replay Bumps from the Workout History screen, go to your Recent Activity, scroll down and tap on "Bumps" (see pic 2 below).  This will take you to the Bumps screen for that workout (see pic 3).