Question

What aspect of the structure of the alkene does ozonolysis not tell you ?

Short answer

It doesn't say if the double bond is in the E or Z configuration.

Step-by-step solution

Definition of ozonolysis - 

When an alkene is treated with ozone (O₃) at a low temperature, the double bond's s and p bonds break, and the carbons that were previously doubly bound to each other are now doubly bonded to oxygens. Because the number of CO bonds rises, this is an oxidation reaction known as ozonolysis.

Reductive ozonolysis is the process of converting an alkene into two carbonyl molecules.

We can have cis/trans or E/Z stereochemistry if the R groups are different.

1 is a Z alkene if R₂ and R₄ are the higher priority groups.

2 is an alkene of the type E.

Both, however, produce the same ozonolysis products.

Reductive ozonolysis cannot discriminate between cis-but-2-ene and trans-but-2-ene.

Conclusion-

The only ozonolysis product in both cases is acetaldehyde.