The plugs are obscured by the intake manifold at the front of the engine. This has to come off first. See attached picture which shows a plug after manifold removal.
I understand that the Ducato 2.2 litre engine is based on the Ford Puma engine. If you are wanting to change the glow plugs, the following link leads to a relevant thread on the Transit Forum, which contains some advice.
Hi thanks to Anthony489 and Communicator for your replies they have been really helpful. My son managed to change all 4 plugs, 1 was intermittent and the other 3 were completely dead, no wonder it was struggling to start. Best wishes. Tony