The first thing to do is to send and open the .kml file from ForeFlight in Google Earth on a PC or Mac.
Once the Track Log is showing within Google Earth, you will see the track information, but no specific altitude numbers. To view the altitude information pane, go to Edit > Show Elevation Profile.
Image 1: Edit > Show Elevation Profile.
If "Show Elevation Profile" is selectable, you will see the elevation profile as pictured in image 2.
Image 2: Track Log with Elevation Profile showing.
If "Show Elevation Profile" is not selectable (See image 3), then we will need to perform a few more steps.
Image 3: "Show Elevation Profile" is not selectable.
On the left side of the Google Earth window is a pane with a "places" section. Expand that section. Your Track Log should be listed under "Temporary Places." Expand the Track Log to view the sub-items. You will see a "Start" icon listed. If you deselect all the items in the Track Log (image 4) and then reselect only the box that says "[no name]" you should be able to select the Elevation Profile (See image 5). If the "Start" box is selected, the Elevation Profile will not be available.
Image 4: All items deselected
Image 5: [no name] is selected after clearing all selection. Now Elevation Profile can be viewed.
It is important to note that if you just deselect the Start icon only, that will not work (See image 6). You have to deselect all, and then reselect only "[no name]".
Image 6: Only the Start box was deselected without deselecting other boxes first - this will not allow the "Show Elevation Profile" to display.
Once you are able to select "Show Elevation Profile", do so. You will see a profile as follows in image 7.
Image 7: Elevation Profile is displayed for a Track Log
Alternatively, you can just delete the Start line by right clicking and selecting Delete (See image 8). Once that is done, and with the Track Log selected, the "Show Elevation Profile" should be available to select.
Image 8: How to delete the Start line
Of interest, the Profile shows both speed and elevation. To view only one or the other, tap on either the red elevation box or the blue speed box in the profile view. Image 9 shows just elevation selected.
Image 9: Profile view shows only elevation information when speed is deselected.
Last, you can scroll across the profile with your curser to show specific information for that point on both the profile as well as on the track (See Image 10).
Image 10: Scroll with curser across profile to view point specific information.