The external conflicts in this story mostly center around the extreme survival situation that Pi finds himself in. He has to worry about battling constant danger and impending death while he is on a lifeboat at sea, with a tiger. Richard Parker himself is an external threat, a 450 pound animal that brings conflict into his life; Pi has to constantly worry about how to manage him and maintain control. The weather--sunshine, waves, storms, the cold at night--is another external conflict. Lack of food and water is yet another. All of these are external conflicts that consume most of Pi's everyday moments, and loom huge in the battles he faces. At the end, he has the conflict of his Japanese interrogators not believing his story.
Pi's internal conflicts also relate to the situation that he finds himself in. He battles his own fear of Richard Parker, fighting off total terror in order to prove he is the "Alpha" male on the boat. He has to battle hopelessness, and trying to maintain a degree of faith and hope during the rather depressing circumstances he faces every day. He questions God, and battles internally over issues of religion and why God would have let this happen to him, and what meaning there is supposed to be in all of it. He struggles internally with the will do live versus the will to die--each day he has to convince himself, internally, that the day is worth living, in order to motivate himself to go on.
Considering Pi is the main and solo character in most of the novel, there is quite a bit of conflict to keep the plot active, and to show Pi's resiliency in a very difficult situation. I hope that those thoughts help; good luck!