If one is not of humility, how then does God hear his prayers asking for it?
I'm not sure I understand what you're asking.
God hears all prayers.
But the very desire for humility is a good which (like all goods) comes from God. Thus the man cannot begin to ask God for humility unless God first give that man the desire for humility. The man, having received the desire, then asks for humility. And God might or might not give it to him.
Yes, to even ask for humility presupposes a certain level of humility, from which one can ask for an even deeper level of it.
To pray at all presumes a certain degree of humility, insofar as it's a confession that you are in need of help.