"I can't tell you exactly, any more than I could tell you exactly what is the experience of sex if you have never had it." (1.82)
Perhaps this explains why the boy still wants to be a vampire, even after hearing Louis's story. There will always be a difference between even the best fiction and reality. You cannot truly understand something until you've experienced it yourself.
"How pathetic it is to describe these things which can't truly be described." (1.96)
This is a strange statement, because if Louis actually believed this, we wouldn't have a book. That is what Interview with the Vampire is: a book that tries to describe things that can't truly be described. Does trying to discover this knowledge make a person pathetic?
"Why did you become a vampire? [...] And why such a vampire as you are!" (1.347)
One secret that Louis wants to know is why Lestat is such a jerk. We're not sure if this knowledge even exists in the world, but we do know that not all vampires are power hungry bullies.
"I was educating Claudia, whispering in her tiny seashell ear that our eternal life was useless to us if we did not see the beauty around us." (1.427)
As Claudia's father figure, Louis is responsible for educating her. It's a good thing he is there to instill in her an appreciation for beauty. If Lestat were her sole parent, we can bet she would be a 100% killing machine. (And that brings us back to another question. Evil: nature or nurture?)
"Suppose the vampire who made you knew nothing, and the vampire who made that vampire knew nothing [...] and so it goes back and back, nothing preceding nothing, until there is nothing! And we must live with the knowledge that there is no knowledge!" (1.511)
One benefit to being a vampire is that it's easy to trace the history of the species. Why? Well, they live for a heck of a lot longer. It's possible that the very first vampire is still alive somewhere. The very first human, on the other hand, is no more than dust.
"There was in me that great desire to see Europe and to know it." (1.651)
Louis wants to visit Europe for two reasons: 1) It's the mother of New Orleans. He wants to see where the history of the great city he loves comes from. 2) Claudia's books practically have maps in them that say "Here Be Vampires" right over Europe.
"'[Louis], that knowledge was our birthright, and [Lestat] deprived us.'" (2.25)
One way Lestat holds power over Louis and Claudia is by withholding information from them. This kind of backfires. In fact, Louis and Claudia put the fire in backfire when they burn Lestat, fed up with him. What does this tell us about the power of knowledge and information?
"'Where do these vampires come from!'" (2.126)
Louis and Claudia go to Eastern Europe to find information about where they came from. In Eastern Europe, they find a creepy branch of the vampire family tree: the horrific Revenants. This knowledge doesn't help them in any way (or does it?). It just muddies the waters further.
"'Love's blinded you, your fascination with his knowledge, his power.'" (3.248)
One of the main reasons why Louis is attracted to Armand is that he's a veritable font of knowledge. Unfortunately, Armand turns out to be just as manipulative as Lestat is. And since he's not as brainless as Lestat can be, that makes him considerably more dangerous to Louis.
"'It's as if you've cracked a door for me, and light is streaming from that door and I'm yearning to get to it, to push it back, to enter the region you say exists beyond it!'" (3.433)
This is a good metaphor for seeking knowledge in general. Sometimes you don't even know something exists until someone shows you a little piece of it. Then you can't get enough.