In general, effects that trigger when a card is sent to the graveyard can only be activated when that card is actually sent to the graveyard. This is because the effect is specifically tied to that event.
However, there are some exceptions:
* Cards with "if" or "when" effects: Some cards have effects that trigger under specific conditions, such as "When this card is destroyed." If the card is destroyed and sent to the graveyard, the effect will activate.
* Continuous effects: Some cards have continuous effects that are active while they are in the graveyard. These effects can activate even without being sent to the graveyard, as long as the card is in the graveyard.
* Special rules or card interactions: There might be specific rules or interactions in certain card games that allow you to activate an effect that isn't explicitly tied to being sent to the graveyard. For example, some cards may allow you to exile cards from the graveyard, triggering effects that activate when a card is exiled.
To determine if you can activate an effect that doesn't say "when this card is sent to the graveyard," you need to carefully read the card's text and consider the specific game rules.
Please provide more context about the card and the card game you are playing so I can give you a more accurate answer.