I have two questions:
1. In an interaction, I'd like to find out the position of the object my sim is interacting with, in terms of height.
If I could find out whether the object is on the floor/ground, on an endtable, coffee table, table/counter or other, it would the sufficient.
Could I make a test for the category of the object container object, or somesuch? Do these types of surface objects have separate categories, and if they do, how do I find the numbers?
OK, it seems that posting the problem to MTS works wonders to one's brain. I have figured this out.

2.
I'd like my sim to look at the object it is interacting with, but 0x006E Look at (Target: Stack Object ID 0x0000, default 3/4 height) is giving me an Undefined transition error. (So does 'custom look at')
My object is using PaintingGlobals just like the deco object I got these BHAVs from, but obviously something more is needed.
The problematic nodes are nodes 3 and 4 in BHAV 0x0000101A.
Please help?

3.
The Init for the AL wall shelves does not set a category. Even if it did, how would I find out how high the shelf is at the moment of testing?

Any chance you could attach a copy of the error log you're getting?

As for finding out where something is in game, one option would be to look at the object which currently contains the Stack Object (ie, "Stack Object Id := Stack Object's container id") and check its category.