Klout uses rating algorithms and other semantic analysis to determine a score reflecting how users of social networks are influencing their followers, and those already using Klout to chart their progress on Twitter and/or Facebook can simply add LinkedIn via the Klout dashboard.
More details in a short Q&A from The Official Klout Blog:
Q: Who will have LinkedIn integrated into their profile?
A: Everyone who has connected their LinkedIn account to Klout. If you want to add your LinkedIn influence to your score, it’s available on the dashboard.
Q: How will the LinkedIn integration show up on my profile?
A. Your LinkedIn influence will be added to your score, and statistics from your LinkedIn profile will appear in the score analysis section.
Q: How will connecting LinkedIn affect my score?
A: Your Klout score will be more accurate. For instance, you may not use Twitter or Facebook that much, but you may have a rich and engaged network of professional contacts on LinkedIn. There is no risk that your Klout will go down. In most cases, users will see a score increase, even for infrequent LinkedIn users. Once you’ve connected LinkedIn, your score will be updated in 72 hours or less.
Klout would not specify to TechCrunch the process it would use to analyze data from LinkedIn, saying it would focus on interactions, who users are interacting and engaging with, and content shared with contacts.