Right click on the block. In the menu that pop-up menu, the identifier within the parentheses next to Block Parameters is the type of the block.
Or, click on the block to highlight it, and then at the the command line:
get_param(gcb,'BlockType')
Unfortunately, and this is annoying, it's not straightforward to find that block in the Simulink Libray Browser, at least in my version of Simulink. I don't know why there isn't a way to do that, similar to the Libray Link option for library blocks. Oh well. If you need to find it, you can right click on the block, click Help, and the doc page contents shows which library contains that block.
