How to use query language?


first of all: is there a good example how to use query language?
i only found this Query Language | Kirby CMS
and in these examples are no folders.

How do i know what’s in the site and page object? is there a way to display the whole object in yaml?

Here is my problem:
The screenshot is from the blogpost blueprint.
When i’m looking for the “rma” folder it is working, but i’m trying to find the blog template without using the hardcoded way.
I tried several ways (as you can see in Line 38-40), but it wasn’t working. I always get an error in the panel or the options are empty.

      en: Category
      de: Kategorie
    type: select
    max: 1
    options: query
    query: page.parent.parent.find("rma").blogCategories.split
#    query: page.parent.parent.filterBy("template", "blog").blogCategories.split
#    query: page.parent.parent.template("blog").children.blogCategories.split
#    query: site.children.listed.template("blog").blogCategories.split

Thanks in advance for your support.

Best regards,