"New" actions in Salesforce1 may occur in two different forms.
- The standard New button, which serves the full page layout appropriate for the record type and profile
- A Create a Record quick action, which has its own layout.
Any actions in the action bar for Account that create child records (e.g. Log a Call, New Contact, New Event) are usually quick actions. You can customize the layouts from Create > Global Actions > Actions for global actions (I'd try there first, as I suspect the action you're looking for is the out-of-box New Event action), or from Customize > Account > Buttons, Links and Actions for object-specific actions.
The New actions that appear once you drill into a related list from the Account record in Salesforce1 are usually the standard New buttons. However, the standard New Task and New Event actions don't appear on the Open Activities related list in Salesforce1, so you won't be able to use the page layout version for New Event.