Any chance of seeing its current enclosure setup?
We are all more than happy to help, but you need to realize that most on here are very protective of all animals, and there are some people that will purchase before thinking, resulting in the animal being held in an enclosure too small, too cold or too hot, wrong substrate, wrong food etc.
Not saying that this is the conditions your cunningham is being subjected to, but there are some out there who, put honestly, just don't care.
Without knowing the locality of the skink, I would recommend a 4ft x 2ft x 2ft enclosure. This will suffice all the way up to adulthood. If you decide to add another for breeding however, you may want to start looking at a 6ft long enclosure.
I have never kept Cunninghams, so I can't comment on food, temperment, etc.