In order to check on which stage a task for a certain user are, you need to go to user’s profile. In «Completed tasks» section you will see tasks for all processes, which have been performing for this user, including incomplete ones.
In a field you can see all stages of this task performance.
Here a date of its creation and its accomplishment on each stage as well as action name are indicated.
In «Result» column you can see a detailed description of result achieved after finishing of this stage.
In «Who» column a manager/a performer of this stage is depicted.
Mind that task history contains only last 1000 stages.
If process is not completed (for instance, there is a delay before next letter (postponing), then a task has «Postponed» status. You can see it in «Tasks» section as well as in user’s profile.