Wanted to know if i can use the theme in one liferay workspace to another in liferay 7.2.    If yes Could you please let me know the process. 

You mean, you want to have the same theme in two Liferay Workspaces?
As a workspace is a single directory hierarchy, I can see two options (and strongly prefer the first):

• Store it in your version control system and check it out in both workspaces
• Provide a link for the theme's directory into that other workspace's directory

But, after all, I don't see that intense of work within a theme once the CI is nailed - If you find yourself constantly tweaking the theme, you might work on the wrong abstraction layer. The theme doesn't need to be in the workspace, you can just build a deployable theme and deploy it to as many machines as you like - without having constant development access