Essays on the goodness of God must really include a discusssion of the Euthyphro dilemma See the PowerPoint if you are in doubt about this.
Creation – how is the idea that God is good – shown in the creation narratives – not simply those in Genesis but also the ones in Job 38 and in several Psalms, especially Psalm 104.
Law and Covenant – your examiner is very keen on this idea. The ten commandments show God’s goodness in the personal and social life of mankind. The whole idea of covenant – that binding agreement between God ad man, shows how God cared for Israel, despite the fact that at various times in their history they rebelled against him.
Jesus – the goodness of God is seen in the fact that God’s son was born at all, let alone in some of the things he did. Don’t overlook the crucifixion. Can the goodness of God include the crucifixion? Think of it from the point of view of a Christian who will say “Christ died for (on behalf of) our sins.
Christianity – the goodness of God is all about human reconciliation with God, redemption of the world by Jesus, through his death, the concept of grace etc. Take your time over these they are quite complicated.