Based on the country you are looking for the certification, rules may be slightly changed. For India following syllabus is applicable (Source: atcguild.com)
At present it is a year-long ab-initio training (Under revision to make it in two sections of six months each)
Modules:
- Air Traffic Services
- Aerodromes and Ground Aids
- Air Legislation
- Meteorology
- Communication Procedures
- Technical
- Search and Rescue
- Air Navigation
The selection shall be made on the basis of a
- Written test
- 50% questions on subjects relating to educational qualifications
prescribed
- 50% on General Knowledge, General Intelligence, General Aptitude,
English etc. Voice test
- Personal Interview
- Medical fitness as per ICAO Annex-1
I Googled for the subject, but didn't find much information on the paper patterns or example papers.