There's no single "educational qualification code" for the Combined Defence Services (CDS) Exam. The eligibility criteria are specified in terms of educational qualifications themselves, not codes. You need to meet the specific educational requirements as outlined in the official CDS notification released by the Union Public Service Commission (UPSC) for that particular exam cycle. These requirements will vary depending on the specific entry (IMA, INA, AFA).
To find the exact eligibility criteria, you must refer to the official UPSC notification for the CDS exam year you are applying for. The notification will clearly state the minimum educational qualifications required for each branch (Army, Navy, Air Force). Don't rely on unofficial sources for this critical information.