As a skilled worker, you must have a vocational qualification or university degree. You do not have to be a recognised skilled worker to apply for the Opportunity Card. Instead, you must prove that you have completed (at least) two years of vocational training / a university degree according to the rules of your country of origin. Certificates of completion or written confirmation from your employer or training institution can serve as proof.
This does not apply to IT professionals, who do not have to prove a university degree or vocational training, but must demonstrate two years of professional experience and provide an existing employment contract. You can have your professional qualification subsequently recognised in Germany via a recognition partnership. If you do not have the relevant documents needed for proof, a qualification analysis may be an option.