Professor Onyx

If an effect creates a copy of an instant or sorcery spell, this will also cause the magecraft ability to trigger.

For Professor Onyx's last loyalty ability, "this process" is the following: First, the next opponent in turn order may choose a card in hand without revealing it, then each other opponent in turn order does the same. Then all the chosen cards are revealed and discarded at the same time and each opponent who didn't discard a card (whether they chose not to or had an empty hand) loses 3 life. This all will happen seven times, for a maximum loss of 21 life per opponent.

Some effects instruct you to copy an instant or sorcery card in a zone other than the stack. These copies do not cause magecraft abilities to trigger. However, most effects that do this also allow you to cast the copy, and casting the copy will cause magecraft abilities to trigger.