Content in usually split in two parts: introtext and fulltext (it's a terminology that's stuck since the early days of Joomla)

If you pasted your content in the Joomla WYSIWYG editor without using the "read more" button in the editor to insert a split point, then this means you only have "introtext".

Since in K2 you have full control of the display of content, you can essentially have different display criteria per category or item "view". In other words, you can choose to show only introtext in the category listing view and in the item view choose to show both introtext and fulltext (check the K2 blog as a good example - getk2.org/blog).

In your case, I'm guessing that "introtext" is displayed in category listing views and only "fulltext" in item views. You probably did not "split" your content with the "read more" button in the Joomla WYSIWYG editor and as such, there is no "fulltext" to display in the item view.

You need to request some clarifications on how the site was setup in the first place and what you should do to have your content show up properly.

There is an easier way for you. In K2's component settings there's this option jmp.sh/lqle6d0 that you can switch to "No", in which case the item edit form will now show 2 distinct editor blocks, one for introtext and one for fulltext.

Perhaps this is simpler for you.

Great!