This toy is what I know it is. / This toy the thing which I know it is

Judging by the phrasing in the question, this may not be your first language. Neither of the two options provided make complete sense, and sound a little odd. You could say: "I know what the present is; it is a toy" or "I know the present is a toy" or "The present is a toy and I know it" I'm not really getting what concept you're trying for.