foundry/Data/systems/pf2e/templates/items/action-details.hbs

{{> "systems/pf2e/templates/items/partials/ability-activation.hbs"}}

{{#unless (eq item.system.actionType.value "passive")}}
    {{> "systems/pf2e/templates/items/partials/self-applied-effect.hbs"}}
{{/unless}}

<div class="form-group">
    <label for="{{item.uuid}}-death-note">{{localize "PF2E.ActionDeathNoteLabel"}}</label>
    <input type="checkbox" name="system.deathNote" id="{{item.uuid}}-death-note" {{checked data.deathNote}} />
</div>