Hi Rajat...
Do you mean you're interviewing someone for a job as a Migration Expert for Windchill ProjectLink and PDMLink (as in a consultant). Or are you interviewing someone for a position as a Windchill ProjectLink and PDMLink Administrator?
In my mind there are three types of people with a good bit of overlap between them:
1. Windchill System Administrator
2. Windchill Business Administrator
3. Windchill Migration Specialist
The Migration Specialist is a different kind of animal (not literally an animal but you get the idea). They have special skills required to migration from Pro/INTRALINK 3.x (sometimes multiple systems) to Windchill. Many of these skills are only required and only necessary during a migration effort. Thus, they are highly specialized. There's a huge variation between migration specialists. Some are fairly well terrible. A select few are really wonderful.
All of them are a bit crazy. 
Again, in my mind the Windchill System Admin understands what's going on under the hood of the system. This person would understand how to manage and upgrade the system, Oracle, network resources, and other intricacies of Windchill.
Finally, the Windchill Business Admin understands how to manage the everyday functions of Windchill. This person might be a tech support person or trusted admin with the ability to delete files, make new projects, handle file security and permissions changes, etc. This is more of a light administrator whereas the system admin is much heavier.
Your post seems to suggest you need a migrator... but I am not sure. Which are you trying to find? And, if it's a Migration Specialist, I shudder to think of the minefield you're wading into!
Regards,
-Brian
