To prove that it is not a tautology, we need to show this proposition should result as FALSE.
To make it as FALSE in implication (ex : x->y) , we need to prove x as TRUE and y as FALSE. Here x = (not p ) OR q and y = q->p.
To make y as FALSE , we need to definitely have q = TRUE and p = FALSE.If we give that , the resulting truth value of this proposition is FALSE.