How we will get to know which career site is using which template?

You can check which career site is using which template in the career site editor. Where in the Theme tab you will see the currently used template is indicated at the top.

Navigation: Setup and Maintenance
Setup: Recruiting and Candidate Experience
Functional Area: Candidate Experience
Task: Career Sites Configuration
Edit Site
Theme tab

I hope this blog post was helpful for you. If you have any questions or feedback, please leave a comment below.