I am looking for a SCJP MockTest, free or fee, but it must have explanation why this answer is wrong or right , any recommendation ? Even certified already, I want to renew my knowledge of 1.5 / 1.6.
You won't find very detailed explanations on any mock tests. In my experience, if you are confused over a question, then looking at the docs, googling and asking the question here at javaranch should be enough to clear the concept...