Currently, if the task Assignee is not the Submitter or the Approver on the request associated with the task, the Assignee cannot view the request details. 

Adding the ability for task Assignee to view the associated request is already planned out in our product backlog, however we have no committed timing for the enhancement at this time.

As a workaround, the Submitter, Approver, or Request Admin can pull a printed PDF of the request to supply to the task assignee if they do not have access to the request. 

Another option would be to assign the user(s) a Request Viewer role. However, this option will allow the user(s) to see all the requests in the system.