In the next release of JFBConnect, we'll automatically be adding the app_id tag to all pages (when Open Graph integration is enabled). To do it now, for both parameters, we recommend going to the Social configuration area, clicking on the Open Graph tab, and making sure Open Graph integration is enabled. Next, use the big area below that for setting the defaults and enter:
app_id=12345
admins=12345,654321,88888,etc
Yes, you should set your App ID for the application used on your site (as set in the Facebook API tab).
Regardless of these settings, likes will automatically be for your site. All Likes on your page are tied to the URL that was liked. This occurs regardless of the Open Graph tags. However, JFBConnect does do some checks and extra things to make sure the URL is the 'best' URL to be liked (by removing unnecessary query strings and other things that could make non-unique URLs). All of this is meant to focus your Likes on the proper page, instead of spreading them out among multiple URLs that work for the same page.
Finally, for SEO benefits, I believe Bing is the only search engine that has stated they use Like data to modify rankings. Google currently (and likely will not in the future) use this for rankings.
As for K2, if you're already setting the title and description in K2, JFBConnect will automatically use those for the Open Graph values as well. You may want to set a default type and image in the defaults area, as above:
image=http://site.com/default-image.jpg
type=webpage
Then, in each article, you can override any of these settings (title, description, image, etc) with our easy-tags:
{JFBCGraph title=Best title for article}
{JFBCGraph image=http://site.com/best-image.jpg}
Hope that answers your questions!