What is a correct : "Read it yourself," "Read yourself," or "Read by yourself" ?
'Read yourself' is unnatural.
The others work depending on the context.
There's also 'Read it for yourself'
How do you want to use the expressions?
Rover
Without any additional context to go on, they are all correct. However, please note that my suggestions are not the only possibilities for each of your examples - there are others.
"Read it yourself". You read the document yourself.
"Read yourself". Read on your own, without help.
"Read by yourself" Read alone.
John