The answer to that would depend upon what kind of skills matrix are you looking to prepare and what sector do you work in?? The skills matrix and its contents would differ depending on the above two facts.
Your skills matrix can include only technical skills like expertise level in various software applications and it can also include soft skills like Communication skills, Time Management skills, etc.
To cut it short, it all depends on the sector you are working in and what are you looking to assess by means of the skills matrix that you make.