To display the parent company's activity on the subsidiary's form, you could create a related list on the subsidiary's form that shows all the related activities of the parent company. Here's how you can do it:
1. Create a lookup field on the activity object that links to the parent company's account. This will allow you to associate the activities with the parent company.
2. Create a custom related list on the subsidiary's form that displays the related activities based on the lookup field. You can do this by going to the page layout editor for the subsidiary's account object, and adding a related list to the page layout.
3. In the related list properties, set the related object to be the activity object, and set the filter criteria to show only activities that are associated with the parent company's account through the lookup field.
Once you've completed these steps, the related list will display all the activities associated with the parent company on the subsidiary's form.
Alternatively, you could also create a custom report that shows all the activities associated with the parent company's account, and then add a report chart to the subsidiary's form that displays the report data. This would allow you to display the activities in a graphical format on the form.
