Good morning. Please review these resources:

You can choose software encryption:
https://documentation.commvault.com/11.24/expert/7764_software_encryption.html

Hardware encryption:

https://documentation.commvault.com/11.24/expert/7794_hardware_encryption.html

Do we have any extra license for encryption?

Is Commvault encryption is better or the from Tape Library side 

@Kavya , it depends.  Having CV handle it means you have it all centrally located.  However, the hardware side might be faster.

Depends on your preference and needs.

Does that mean if we enable encryption from the Commvault, the job take longer time than usual to run?

Any encryption will add overhead (it’s an extra process that has to run), though how long/how impactful; is subject to a host of factors.

My suggestion is to run a medium/small backup with no encryption, then with CV, and again with hardware and see how long each one takes.