ERROR: This page is using an unprefixed version of template {{Documentation/docname}}

Create {{Wn/nia/Documentation/docname}} instead and replace all occurences of {{Documentation/docname}} in Wn/nia/ prefixed pages by that.
You may like to check 15 templates in Category:Wn/nia/Templates using unprefixed template Documentation/docname first to remove all occurences from those templates which will fix the pages containing those templates too.
Template:Wn/nia/InfoboxStart/doc|action=edit&preload=Template:Documentation/preload}} create]]
Template-info.svg Template documentation