Thunderbolt Display magnetic edge?

The screen is held on with magnets so it can be easily removed for service. Not sure about attaching more magnets to hold notes (I would not).

I believe the only magnetic areas are where the built-in speakers reside.

There are magnets at several locations under the front glass screen.

Yes, two speakers on the sides and a miniature subwoofer in the middle (source: iFixit).