Eg I have a block that is on the page to edit the purchase order, both the editing page of the order as the "block" passes through the event sales_order_load_after when obeserver the event can not know what they spent for the event, if it was page or block.
How to know who called or went by event?
You can use a PHP backtrace function like debug_backtrace or Magento's own backtrace: mageDebugBacktrace.