I wish him luck and hope he enjoys the experience. I have been involved in junior football for many years and have seen loads of promising players be taken for trials and the vast majority end up disappointed. He may find when he gets there that there's around 50 trialists there and only half a dozen or so will be asked back. Those that get through the trial may then get a few weeks, after which they are usually discarded. Some are kept on but often just to make up the numbers as the club is really only intersted in a handful of special players, often from overseas.. The chances of making a career are very slim indeed. I know England schoolboys who were considered as potential greats who were on the scrapheap a year later.
I wish him well!