I wondered about that after I hit send actually. The documentation on personal tasks does say it's 'available only to you'. As an admin, you can see anything, so you're still able to access them. If I look at a personal task I created myself, I do see the Sharing ability which indicates that security is likely still the culprit. You could train the user to go share his tasks, but that seems cumbersome.
You could have him set up one specific 'My Ad-Hoc Work' project and assign all his tasks to it, which would give you the ability to share that project with his manager as well. (This is how I manage my own workload.)
Both of those options leave open the possibility for human error though, which I dislike. From there, the next best option is to trick the report itself into thinking whoever is looking at it /is/ that user.
On the report in the upper right corner, there's a 'Report Settings'. The screen that opens up will give you the 'Run this report with....' option. Put your user into that menu, and anyone viewing the report will see what they see.
Depending on what information you're revealing in that report, be careful with the report security though. Ex. if this person happened to be HR, you might want their boss to see the employee entry/exit interviews scheduled, but probably not anyone who can find the report.
Katherine