How to correctly write the condensed formula for salicylic acid
Some people say $\ce{CHCHCHCHC(OH)C(COOH)}$ Or $\ce{(CH)4C(OH)C(COOH)}$


Both of these are definitely wrong since it seems to indicate some sort of alkene. 


  Others say $\ce{C6H4(OH)COOH}$


This is much better since it "hints" that $\ce{C6H4}$ is a benzene ring. With only 4 hydrogens and what seems to be two substitution groups that fits. Note there is no indication of the relative position of the groups. So this would represent either 3-Hydroxybenzoic acid or 4-Hydroxybenzoic acid as well. 

The basic empirical formula would be $\ce{C7H6O3}$ which would represent probably dozens of molecules. 

So the best way to denote the particular molecule specifically is to name it, or to draw out the whole 2D structure.