How to mask the data in workbench job ?

I believe what you're looking for is the ability to Obfuscate Values so that the users just see a masked field of gibberish, unless they have the explicit password to unlock it.  There are a couple pages that review the process, which is slightly different depending on the version of Workbench you're running.

Encrypting, Decrypting, and Hashing Workbench 5 Data

Encrypting and Decrypting Workbench 4 Data

It's a nice feature, but its biggest shortcoming is that a user with the permission to unlock/unmask the protected data can only view that unmasked data in Sumo cards.  You can't use the unmasked data in visualizations.