Hi @Deirdre, are you referring to the Calendar that is found under the Productivity section of the marketing portal? As far as I understand, this calendar can only be filtered by content or task type (e.g. blog, email, recurring email, landign page, social) as well as by campaign. It doesn’t appear possible to filter by who that particular assignement is tasked to within your oganization.
However, if you are talking about the “Tasks” in the Sales side of the portal, you can customize your task view to filter by task assignment.
Hope this helps!