Does a spell with split second stop triggered abilities from going on the stack?

Split second (CR 702.61) restricts what players can do while the spell is on the stack — specifically, no player may cast spells or activate abilities (except mana abilities). It does not prevent triggered abilities from triggering or being placed on the stack, because triggers are automatic game events, not player actions.

CR 702.61b states explicitly: 'While a spell with split second is on the stack, players can't cast other spells or activate abilities. Triggered abilities can still trigger.' The game engine places triggered abilities on the stack as a rule process, not as a player action, so split second cannot stop them.

Note that mana abilities are also still usable during a split second spell, since CR 702.61b carves out that exception as well. Only voluntary player-initiated spell casting and non-mana ability activations are locked out.

Concrete example: You cast Sudden Shock (which has split second) targeting a creature. Your opponent controls a creature with a 'whenever a spell targets this creature' trigger — that trigger will still trigger and be placed on the stack even though split second is active. Your opponent just can't cast Giant Growth in response to save it.