I could find the path for AEM 6.4 this is "/libs/granite/ui/components/shell/page/page.jsp" . Though, thanks for your help leading me into right direction. Let's hope to find the right path for AEM 5.6 either.

Thanks for your answer. I have beeing investigating further and found /libs/cq/gui/components/authoring/editors/core/head.jsp as a source for the edit mode. The requirement got an specification for creating a dynamic title.

Hello,I've got an requirement to change the page title from Authors user interface. The default title in AEM 6.4 is "AEM Start", in AEM 5.6 is "AEM Projects".Is it possible to archive it, if so how? Thanks in advanced. 

Some associates there works also with AEM faced the same situation. They have also no explainnations for this strange behavior. They think there are not documented changes in Service Pack 6, so thier recommendation is using like operator instead of contains

My question to key word contains is similar to yours. See https://experienceleaguecommunities.adobe.com/t5/adobe-experience-manager/sql2-query-with-contains-does-not-find-any-nodes. Will it help if you use the like operator instead of contains?

Based on https://experienceleaguecommunities.adobe.com/t5/adobe-experience-manager/search-inside-a-page-content-and-the-content-of-the-content/qaq-p/380627 is possible that contains looks only in nodes from type 'cq:Page' and not in other node types? That wold explain this strange situation.

@Jineet_Vora I think you haven't understood my question right. And I haven't marked this as solution (whoever it was).

If I look into jcr:title I will get a result with contains, other node properties do not work. Any ideas?

Thanks for trying to help. I tried your suggested query and the result list is still empty. Update: It seems only the property jcr:title returns a non empty resultlist. What  a hell?

I do not understand the difference for my case. What I know, if you use contains it looks for exact matching. So you can define more than one pattern to find occurences. While with like is allowed to use wildcards (the % sign). My provided example has an exact match, or not?