Re: Showing only certain categories in the sidebar / adding a second categories box
"this" does not refer to a category so there is no "pos" for it.
I am not sure where you are using this "this._category.id" so hard to say what you have there.
In this case you can use "this._category.pos" or "this._category.position" - depends on how it is called within the _category array. You can also try "this._category.getPos()" or "this._category.getPosition()". If none of them works you will have to decorate the appropriate class behind the template and see how to add the category position to each element so you can use it in the template.