According to Soldiers Died in the Great War there were two men called J. Turnbull, both were born in West Sleekburn, both served with the Northumberland Fusiliers, in different battalions, neither rose above the rank of private, both died in 1916.
A “J. Turnbull” is remembered in West Sleekburn on W34.01 and in Newbiggin by the Sea on N10.06 and N10.14
Since it is difficult to identify either without further knowledge, any help would be greatly appreciated.