Please help me figure out following.

I have several K2 items that were not assigned a menu item. At the same time those K2 items are children of a category that has menu item assigned.

Question: When a visitor of my website click on a K2 item that has no menu item, is there any way to activate a menu item of a parent category?

Visual explanation:

Category - has menu item
-- item - no menu
-- item - no menu

User click on item -> Category menu activated

If you have problems with modules use Advanced Module Manager. Even free version works OK with K2.

If you are talking about menu highlighting (active diferent color) disable Cache for all menu modules. Cache make it lose active hightlighting.

What do you mean saying, "If you have problems with modules"?

I am aware about Advanced Module Manager extension. I am trying to avoid adding menu items for each K2 items.