Hiya, been giving this more thought. Don't be put off that he may have been a good deal older. My great aunt married the German I'm researching in 1924 in Glasgow, a few years after he had been released from Knockaloe. He died in his late 40s in 1928. My great aunt was a good 20+ years younger than him.
My Herman must have been granted permission to remain in Britain due to his two Scottish born sons from his first marriage. Herman's first wife, an Aberdonian, died early 1914, just a few months before Herman would have had to report to the police as a foreign enemy alien.
My hope is the new WW1 material will shed some light on where his young boys were brought up while he was detained on the Isle of Man.
I thought about the Valuation Rolls at Scotlandspeople and using the search term 'Sch' in surname and names beginning with 'Jo' in the forename search field. These three are from the 1905 rolls. Joseph Schimdt, tenant at Stables, 30 West Forth Street, Kilrenny, Joseph Schneider, tenant at Dwelling House 119 Meigle Street, Galashiels and Joseph Schulman, proprietor House Richinwood, London Road, Glasgow.
And on the 1915 Valuation Rolls a 'John' Schermeide, tenant 295 South York Street, Gorbals. I know this is not a Joseph or Josef, but bear in mind by 1915 tensions were running high and violence was not uncommon against those perceived to be the enemy in Scotland. Many shops were targeted and many choose to anglicise their names to fit in/cover up their origins.