MyCase lets you easily view and manage the tasks that are assigned to other firm users.
Click on the Tasks tab at the top of the page.
In the filter menu, there is a dropdown menu named Assigned To (pointed out below). Click this dropdown and select the person who's tasks you'd like to view.
A task can be assigned to other people and assigned to you at the same time. In that situation, the task would show up on your task list, as well as the task list of the other people it's assigned to.