Example of work is exactly that, a sample of the work that you are describing. For example, if you were talking about a video service, you may use exampleOfWork to point to a sample video. In the documentation example, they talk about a book, and then the published book with specific ISBN is the work example. The Schema.org description reads: exampleOfWork – A creative work that this work is an example/instance/realization/derivation of. The property was added by the bibliographic extension.