What is the eligibility criteria for SAP LABS?

The most fundamental requisite for anyone who wants to undergo SAP training, is being a graduate. You can be a graduate from any stream, but try to choose an SAP module that is related to the subject which you studied at college.
Actually for learning sap, no prerequisite is required. In most cases if you have only graduation degree then that's enough to learn Sap and get Job
In general, when you apply for a job, it is allowed for the companies to ask if you have applied for this company before and if you got hired. And most SAP subsidiaries do collect this info.
However, there is no rule on how to use this info. So it is largely to the hiring manager’s discretionary to decide if they want to give it a consideration.
SAP Labs judges its candidates much like other product companies. The concentration of the interview is not on the depth of your programming language but your ability to solve problems.
Nowadays, it is commonplace to search for solutions on Google or Stackoverflow and SAP knows that you will do the same even after you join them. So SAP wants to know how you are going to approach the solution instead of what the exact solution is.
So, know your basics, sharpen your problem solving abilities and stay calm.