When you create menu items, the K2 URL router takes action after the menu item alias.

So if you have a menu item point to a specific K2 category (let's call it "Blog") and you don't modify the auto generated menu item alias, then the resulting URL will be: domain.com/blog

If you now click on some K2 item in that /blog page, you go to an item URL that would look like: domain.com/blog/item/5-summer-vacation-is-over

In the above example, the K2 item has the alias "summer-vacation-is-over" and ID 5.

Likewise, if you explore the K2 demo site you'll see something like: demo.getk2.org/magazine/item/217-donec-ut-lorem-sit-amet-eros-217

Depending on your setup, e.g. if you stack K2 categories into multiple levels but only make a menu item to their parent, you could end up with URLs like this (again, taken from the demo site): demo.getk2.org/magazine/itemlist/category/32-architecture

You can of course have a combination of Joomla menu items and Advanced SEF options enabled, but you need to tell me a) what menu item you're creating for K2 content and b) what structure you'd like it to have in the end.

Well it depends on how you've setup things. Is "Advanced SEF" enabled in K2's Settings in the backend, under the SEO tab? And if so, can you make a screenshot of these settings?

If you need help, provide as more info as possible. Otherwise it's a slow guessing game...

Try this: www.joomlaworks.net/forum/k2-en/63421-duplicate-k2-category-listing#179308