Here is how to switch the elevation profile ON in Google Earth on Mac/PC and use other track browsing features.
1. Double tap on the Track to select it and show on the map and right click to show more options.
2. Pick "Show elevation profile"
3. Google Earth elevation profile has a tab with speed calculated by location changes, but you have also a tab #3 (named Speed-R, please tap on it to activate), with speed recorded by speedo/iPhone. That can differ quite a lot in some points from the speed calculated by Google.
4. Use your mouse to move over the speed profile to show value (values for up to 2 selected tabs are shown)
5. Arrow on the map will show point on the track as you move via the speed profile (arrow #5)
6. You can re-play the track in Google Earth by clicking on "play" button.
But, here are pre-requisites. Please be sure to export the track from the track view screen as a Google Earth track:
The speed profile in Google Earth is available only for tracks in "Google Earth Track" format, that corresponds to theirs gx:track syntax.
Tracks exported as gx:track (Google Earth Track) can't be viewed in Google Earth on iPad. That advanced format, that provides speed profiles, is available only in PC/Mac Google Earth versions.