hello
i configure Allowing users to submit content by below link:
getk2.org/documentation/tips-a-tricks/201-allowing-users-to-submit-content
I am using the following things:

1) Joomla 3.6.2
2) K2 2.6.9
I create a menu item for edit form to allow users to submit an article from frontend but item edit form not working
when i click menu redirect to White Pages
excuse me
My English is not good

A white page indicates a PHP error.
Enable error reporting and set it to development so we can see the PHP error.

hello
error repoting:
Fatal error: Call to a member function isCheckedOut() on a non-object in /home/***********/public_html/administrator/components/com_k2/views/item/view.html.php on line 100

hello
error repoting:
Fatal error: Call to a member function isCheckedOut() on a non-object in /home/***********/public_html/administrator/components/com_k2/views/item/view.html.php on line 100

Make sure you overrides are up to date.
If you are not using any custom functionality I 'd suggest that you revert to the default itemform.php

More info on overrides (in your case you need to disable itemform.php) can be found here: getk2.org/documentation/tutorials/174-templating-with-k2-and-the-concepts-of-sub-templates