[Saxon]

If you are laying siege to a castle, you can see the number and general type of magic sites on the main screen. However, you can not see the details. However, if you hit F1 and then look at the province, and then mouse over the site, the name and full description will be revealed.

I a guessing this is a bug, as control of the sites seems to rest with the holder of the castle, but I am not sure.