Does a +1/+1 counter placed by a replacement effect count as a separate trigger?

Replacement effects (CR 614) intercept a game event and modify how it occurs. They do not create a new event afterward, and they never use the stack. When a replacement effect places a +1/+1 counter instead of — or in addition to — something else, that counter placement is simply part of the modified original event, not a separate occurrence that could be 'triggered.'

Triggered abilities (CR 603) are governed by the words 'when,' 'whenever,' or 'at.' They watch for a specific event to occur and then put a triggered ability onto the stack. A replacement effect never generates this kind of event independently; it modifies what already happened in real time.

However, the counter placement that results from a replacement effect can itself be the event that fires a separate triggered ability elsewhere. For example, if a card says 'Whenever a +1/+1 counter is placed on a creature you control, draw a card,' that trigger does fire — but it is triggered by the counter-placement event, not by the replacement effect itself. The replacement effect is not the trigger; it just caused something that a trigger watches for.

Concrete example: Hardened Scales (a replacement effect) changes 'put one +1/+1 counter' into 'put two +1/+1 counters.' If you also control Jenara, Asura of War with an ability that triggers when counters are placed, that triggered ability sees one event — two counters arriving simultaneously — and triggers once. Hardened Scales itself never 'triggers'; it simply modified the event in real time per CR 614.1.

In summary: replacement effects (CR 614) modify events, triggered abilities (CR 603) respond to events. The counter a replacement effect places may later be noticed by a triggered ability, but the replacement effect itself is never a trigger and produces no entry on the stack.