Matthew 17:12

οὐκ ἐπέγνωσαν, ‘did not recognise.’ ἐπὶ denotes ‘further,’ hence ‘clear’ recognition.

ἐν αὐτῷ ποιεῖν. In classical Greek ποιεῖν would be followed by two accusatives. ἐν αὐτῷ in him as the sphere or field of their action.

μέλλει πάσχειν, is destined to suffer, such is to be his experience also. πάσχειν refers to οὐκ ἐπέγνωσαν as well as to ἐποίησαν ἐν αὐτῷ ὅσα ἠθέλησαν.