If its 2174 - Computer programmer, these are the duties listed:
Computer programmers
- Write, modify, integrate and test software code
- Maintain existing computer programs by making modifications as required
- Identify and communicate technical problems, processes and solutions
- Prepare reports, manuals and other documentation on the status, operation and maintenance of software
- Assist in the collection and documentation of user requirements
- Assist in the development of logical and physical specifications
- May lead and co-ordinate teams of computer programmers
- May research and evaluate a variety of software products.
It should be easily interpret-able as you are in the relevant job role - You can take help from friends/ coworkers(In relevant field) to transcribe your letter - Ultimately, as you know, the letter needs come from your employer with a stamp of approval.
If any concerns/ clarifications on interpretation of essential duties, better to consult an immigration lawyer, just to avoid risk of rejection. Normally >60-70% of such duty listing should be good enough. Good Luck!