I think you need CV and letters from current and previous employers to demostrated the work experience.
Very important (Instructions for the 2011 Diversity Immigrant Visa Program DV-2011)
What Occupations qualify for the DV Program?
To determine eligibility based on work experience, definitions from the Department of Labor’s (DOL) O*Net OnLine database will be used. The O*Net Online Database groups job experience into five
"job zones". While many occupations are listed on the DOL Website, only certain specified occupations qualify for the DV Program. To qualify for a DV on the basis of your work experience, you must have, within the past five years, two years of experience in an occupation that is designated as Job Zone 4 or 5, classified in a Specific Vocational Preparation (SVP) range of 7.0 or higher.
How Do I Find the Qualifying Occupations on the Department of Labor Website?
Qualifying DV Occupations are shown on the DOL O*Net Online Database. Follow these steps to find out if your occupation qualifies: Select
"Find Occupations" and then select a specific
"Job Family". For example, select Architecture and Engineering and click
"GO". Then click on the link for the specific Occupation. Following the same example, click Aerospace Engineers. After selecting a specific Occupation link, select the tab
"Job Zone" to find out the designated Job Zone number and Specific Vocational Preparation (SVP) rating range.
Good Luck to everybody