I suggest you find a clear, obvious difference between the two poems first. For instance, a difference could be that in WESSK, the poet talks about the unpredictability of war whilst in Dreamers, the poet discusses the inevitability of death in war.
If you can't do this or there really isn't a difference between the two, then I suggest you discuss the different ways the poets express their similar thoughts in their poems. By this, I mean that let's say you have a similarity. In this case, it would be war. Both poets talk about war and how it is unpredictable, but they do it in different ways.
In both 'What Every Soldier Should Know' and 'Dreamers,' the poets narrow the attention to the unpredictability of war and the lack of control and power individuals have. This is conveyed through the use of the modal verbs in the first poem, where the poet describes how gunshots 'could be for a wedding' or it 'could be for you.' The modal verbs indicate at the uncertainty that war brings, how in some circumstances, gunshots are used to express contentment in celebrations like weddings whilst in other situations, gunshots could be the literal death of someone. This stark contrast creates sympathy towards soldiers as they fight in uncertain situations and are not aware of the enemy's next move which could result in their demise. The poet in 'Dreamers' also discusses the uncertainties in war. However, in this poem, the poet does this through the concept of the helplessness and lack of power of the soldiers. We are told that soldiers are the 'citizens on death's grey land', the metaphor creating the impression that soldiers are the subjects of death. Death is personified to be like a person, implying how death is in fact in charge and what death decides can not be altered by the soldiers, further emphasising the unpredictability of war.
Remember, the question asks you to compare the ways in which the poets discuss/present difficulties. Everyone interprets things differently, so if you can't do the first method, try do the second method I just wrote an example for.