If you are looking for academic research regarding the efficacy or development of CNC training software (often generically referred to as CNCTrain in literature), the following papers are the most cited in this domain.
Because "CNCTrain" can refer to a few different concepts (specific software suites, simulation platforms, or general training methodologies), I have categorized the available literature and key papers below.
The primary advantage of CNCTrain is its focus on without the risks associated with real-world machining.