Hi Monica,
I am a new member and I just came across your posting. It may be too late but I thought I would share my thoughts anyway.
I agree that job descriptions can be a good place to start. The problem is they are often outdated, as you indicated they are at your company. So the best way to identify competencies that are specific to a job is by meeting with subject matter experts. These are people who perform the job on a daily basis. There are many different ways you can collect information from them. You can:
-conduct one-on-one interviews,
-conduct group interviews,
-conduct focus groups,
-have them complete surveys,
-shadow them while they are performing their job.
It's best to gather information through two different methods to make sure it's comprehensive and accurate. It is also good to meet with the managers of the subject matter experts to gather more information about the jobs.
This can be a time consuming process but your results will be valid and reliable.
I hope this helped you.
Lauren