Hermione was screaming again: the sound went through Harry like physical pain. Barely conscious of the fierce prickling of his scar, he, too, started to run around the cellar, feeling the walls for he hardly knew what, knowing in his heart that it was useless.
"What else did you take, what else? ANSWER ME! CRUCIO!"
Hermione's screams echoed off the walls upstairs, Ron was half sobbing as he pounded the walls with his fists, and Harry, in utter desperation, seized Hagrid's pouch from around his neck and groped inside it: he pulled out Dumbledore's Snitch and shook it, hoping for he did not know what - nothing happened; he waved the broken halves of the phoenix wand, but they were lifeless -
Harry Potter and the Deathly Hallows
I don't understand "for he hardly knew what" and "hoping for he did not know what". They look an incomplete clause to me. is there anything omitted? Can someone help explain them in the context?