What is the structure of 92 m/z fragment for aspirin
This spectrum is recorded using electron impact. That means that the molecule is positively charged by losing one electron. 
Since that is a very unstable structure, the molecule starts fragmenting losing neutral fragments. 
More processes occur, but these are the ones that we see in the spectrum. 
The peaks are the positively charged fragments. 

A fragment with m/z of 92, 93 or 94 is typical for phenolic compounds. 
The aromatic $\ce{C-O}$ bond is very strong and therefore first all the rest is lost. 
In this case the fragmentations are:


Loss of the acetyl group: $180-42=138$
Loss of water from the acid group: $138-18=120$
Loss of $\ce{CO}$ from the acid group: $120-28=92$
Loss of $\ce{CO}$ from the phenolic group: $92-28=64$ 


These are all typical fragmentations. 
The height of the peaks indicate the relative stability of the positively charged fragments.