My friend, who is studying game development at the university, is currently studying programming in OpenCL. What would be a simple project that teaches the most important aspects of OpenCL and can be completed in 50 to 100 hours?
I suggest that your friend implement a document related to the development of the game, so it will be what he could add to his resume and help him get a job in this industry.
eg. it is interesting and approximately 100 hours: http://www.unibas.it/erra/Papers/HiBi09.pdf