Apart from City my other passion is for military history research and I've dug out the following.
John Jackson enlisted in the 7th (Territorial) Battalion Manchester Regiment aged 17 years 9 months at Manchester 8/1/1912. Born Newtown, Montgomeryshire but lived on Mauldeth Road, Withington. He was a cabinet maker employed in his father's business at the same address. He entered the Gallipoli theatre 6/5/1915. He contracted a severe bout of dysentery there 29/8/1915 and was invalided back to the UK where he was admitted to Salisbury Infirmary.
His father was John Jackson and his mother Anna. He married Annie Mabel Ashcroft at Chorlton 18/3/1913.
He was discharged medically unfit for further service 8/3/1916 and was awarded a Silver War Badge because of sickness invalidity. (These were issued to men discharged because of wounds or sickness so that when seen in civvies people would know they'd served honourably in the forces and avoided the 'white feather' taunts). He was also awarded the 1914-15 Star, British War Medal and Victory Medal but these would have been issued posthumously, presumably to his widow.
He died of debility as a result of dysentery 9/9/1917 aged 23 as shown on his gravestone. He left £7 to his widow.
Further research may be difficult because he had a very common name but at least you have something to work on. Which one of his medals do you have?