I find the paper recommended by 1st floor very good.
Basically, GARCH model is a model that "fits" something, not just for the fat tail or asymmetic process. For homoscedasticity, and normal distribution in return series, it also performs good. What you need to test is not the fat tail or the skewness, but whether the model fit the data well both in the sample and out of sample. Mainly, out of sample. The paper by the 1st floor gives several criteria to measure the performance.
In short, my point is that, if you do not see any non-zero skewness or high kurtosis by the GARCH model you estimate, it does not mean that GARCH model is not good. It is the data that does not give these characters. If the data has these characters, GARCH model will surely describe these features. What you need to do is just to test the fitness.