I think this is a rudimentary question, but all the things that I thought would fix it have failed to do so.

I have a site I'm setting up. I have a single K2 item linked from a submenu item. When it is loaded, there are two slashes above the title of the article in the space notated as the K2 itemheader

So on this page:
new.ronadamsentertainment.com/about/the-memphis-echoes

The K2 Item is displayed with the title:
//
The Memphis Echoes

and the code shows:

div class="itemHeader">
//
<h2 class="itemTitle">The Memphis Echoes</h2>

I don't know what is inserting the two slashes. //

I've tried turning off category titles in the menu and K2 item controls but this is not correcting the problem.

Screenshot:
i.imgur.com/nnYAbJh.png

Well, I solved this by going back into the K2 Category that this article was assigned to and assigning it to the current template, instead of using 'default' and that has removed the slashes.

This means that your overrides in the item.php file contain these slashes.
You need to locate them in your overrides and remove them.
This post will help you locate the file: getk2.org/documentation/tutorials/174-templating-with-k2-and-the-concepts-of-sub-templates

As to the exact location in the code, the template's developer will surely know.