It's difficult to predict how Okonkwo will react because it depends on where you are in the novel and what you know of the events so far. Further, as another reviewer said, his reaction is definitely revealed at the end of the novel.

Early in the novel, we see that Okonkwo is extremely masculine and proud. He is afraid of appearing weak, which is why he is the one to kill Ikemefuna when the young man eventually must be dispatched. He is one of the leaders of the tribe, but his own fellow leaders see him as sometimes too extreme. Because of his leadership position and his personality traits, we can guess that he will try to take action against the missionaries when they come in trying to convert the tribespeople to Christianity. Indeed, he does try to rally his people around the cause, but his violent and aggressive actions do not attract the following he wants.

In the end, the rebellion fails, and Okonkwo hangs himself. On the one hand, it makes sense that Okonkwo would self-destruct and come to a violent end. On the other hand, suicide is sometimes interpreted as a sign of weakness, or that he could not handle the changes in his village. Some might say he just gave up and should have kept fighting. Okonkwo's final decision can be seen as an example of his giving up/giving in, or it can be seen as his ultimate dedication to his tribe and to "the old ways."

For me to predict how Okonkwo will react would give away the ending, but I can give you some hints on what to look for in Okonkwo's character so that you can make a prediction.  What have you noticed about his character so far?  Chapter 1 gives some detailed information about him - he was famous in his village for his achievements, he had no patience with unsuccessful men, and the author tells us that he was cut out for great things.  

As events occur, how does Okonkwo tend to react?  Chapter 2 tells us Okonkwo had a fear of failure and weakness, so he reacts to everything with outward confidence, pride, and often anger.

Another important question to ask yourself is whether or not you notice any changes in Okonkwo?  If so, what causes him to change?  If not, why not?  

By analyzing Okonkwo's character traits, it will help you to make predictions of how he will respond to all the events of the novel.  Below is a link to some more discussion of Okonkwo's character.