What are some ways the character Milberry is curious?
I'll list and discuss some quotes below that might be taken as indirect evidence for Berry's potential for curiosity, but to my mind, he's more of an observant person rather than someone who actively tries to find out what's going on. That is, he realizes what's happening around him; he picks up on little details that other people might not notice, but he never asks any questions or attempts any experiments. That's what we'd expect curious people to do; Berry doesn't.
1. "'Besides...the ways of white folks, I mean some white folks, is too much for me. I reckon they must be a few good ones, but most of 'em aint good--leastwise they don't treat me good.'"
Above, Berry is musing on the way in which he's treated by white people. You might say that he's curious about it because he notices that it doesn't quite make sense to him. He never did anything to offend these white people, so why are they treating him so poorly? This is what he wants to know. Consider, also, his statement about how there must be "a few good" white people around. But notice that he doesn't ask around about this or try to satisfy his curiosity, if he is indeed truly curious about it.
2. "But what really worried Milberry at this place was that he seemed to sense something wrong--something phoney about the whole house--except the little crippled kids there like himself because they couldn't help it."
Above, Berry is noticing that things are just not right about the way the summer home is run. He even notices how the landscape itself seems lonely, and how the staff is always cranky and complaining. Berry also observes how Mrs. Osborn's attitude changes whenever she's around Dr. Renfield. Further, he notices how the quality of food improves if and only if the staff members are trying to impress someone:
"Funny how the food ain't nearly so good 'cept when some ma or pa or some chil is visitin' here--then when they gone, it drops right back down again... Po' little children."
However, all of this is still Berry just noticing and not examining or questioning.
3. "Somehow, he thought he wouldn't even stay there and work it if wasn't for the kids... And he made up stories out of his own head just for them--po' little crippled-up things that they were--for Berry loved them, too."
Based on the quote above, you might say that Berry's intuition and creativity are characteristics we'd expect, also, from someone with curiosity. But this wouldn't help you prove that Berry is actually curious.
So what I'm getting at is that, even we read the text of the story very closely, all we'll really find is evidence of Berry's powers of observation, his intuition, and of course, his kindness. But if you're looking for evidence of his curiosity, you'd really have to stretch the existing meaning of the text.