- know how Quantum ESPRESSO works, including its internals
- modify/customize/add/extend/improve/clean up Quantum ESPRESSO
- know how to read data produced by the two DFT engines PWscf and CPV (follow this link for the output xml file schema)
The same category of people should also write this manual, of course.
People who want to know about the methods or the physics behind Quantum ESPRESSO should read first the relevant literature.