The Challenge 2 Input Files and Format description is in Appendix A of the Challenge 2 Problem Formulation.
The Grid Optimization Competition Challenge 2 uses a set of 3 ASCII encoded text files for the input data of each problem instance:
These 3 files are formatted according to common data file formats. Please refer to the Problem Formulation document’s appendices for further detail.
The python Solution Evaluation source code provides an example of reading the input files is available on GitHub: https://github.com/GOCompetition/C2DataUtilities.