How to obtain gene signature of a gene X from TCGA expression-gene data set at level 3. And how to obtain status of a particular mutation of X from such a signature of gene X?

Question

[thwbi09]

I am pretty much new to this area. I have downloaded gene expression data and MAF for a particular cancer type at level 3 and level 2 respectively from TCGA. I just want to check the signature of a particular gene X from the dataset and also check the mutation signature for the same gene X. What pipeline one should follow in such a case?