Is there a notification if someone is using Remote Management to observe my screen? I noticed in my sharing settings that my boss has Remote Management access over my computer, with all options checked (Observe, Control, Show when being observed, Generate reports, ...).

Will I receive any notification when my screen is being observed?
Yes &amp; No. 

If your looking for something like a Notification Center notification, then no. However there is a menu bar item you can add and settings attributed to it that are visual aides that you can see if someone is remotely managing your computer. 

System Preferences > Sharing > Check 'Remote Management' > Computer Settings... > Click on Show Remote Management status in menu bar

Now the Remote Management icon will display in your menu bar. They icon image will alter based on it's current state (i.e., if someone is connected or sharing screen etc) 

In terms of a Notification Center notification, as far as I know, it's not possible with the shipped OS. 3rd Party Apps might be available for your desired feature.