Welcome to the Isle of Man Family History Society! Strictly speaking, this site has nothing to do with the Lancashire Fusiliers but your search engine found it because a lot of Manx soldiers served in the Lancashire Fusiliers. If you read some of the messages, you will find the address for their Museum and the Museum should be able to help you identify where your GGF was when he was killed. Do you know where he is buried? If no, then look at the Commonwealth Graves Commission site. That will give you the area.
Otherwise, you will have to visit the PRO in Kew and look in the so-called Burnt Records (WO363 from memory) to see if his record of attestation has survived. If it has, you are lucky because there is usually a wealth of information therein. Whilst you are there, you can check in the Medal Rolls to see if he was awarded any medals. Finally, if you are very lucky, you might be able to read the regimental war diary for the day on which he was killed. The entries, of necessity, are usually brutally short, but they might tell you that x soldiers were killed on that day whilst doing something specific.