The pronoun himself in the sentence "John himslef should have known better even if Joe did not." is an intensive pronoun.
An intensive pronoun is almost identical to a reflexive pronoun, but they have different functions. Intensive pronouns are used to add emphasis. Like a reflexive prounoun, it ends in self or selves. The pronoun is intensive rather than reflexive because it is there simply for emphasis. The sentence would have the same meaning (with less intensity) without the use of the pronoun.
"John should have known bettter even if Joe did not."