Does your friend have any information on his grandfather already? An area of Scotland where he lived before immigrating? A birthdate etc.? As you probably already know there was a significant portion of Scots who were miners in the late 19th century and few records generated regarding specifically miners as far as I know. Has he searched for his grandfather in census records? That would be the first place I would look. One can generally make an informed assumption on a miner's employer from his place of residence. Also is your friend aware that miners in Scotland moved quite frequently? I would also suggest searching for birth, and marriage certificates if he doesn't have those to help construct a family background. I have researched my own grandfather, a coalminer, an immigrant to America from Scotland, and would be happy to share what I have learned about researching if it would help but would need to know more specifically what he knows and what he wants to find out about his grandfather.