A workitem number is an individual number that is assigned to every job in our system.

With this number, we are able to quickly find the job in our system, so that we can examine and remove reported errors. In current jobs, the workitem number is located in the upper area of your screen, between the remaining time and the fee. 

This is how it looks in the Workplace:

And this is how it looks in the App:

The workitem number of jobs that have been completed can be found in your work history.