If Sanzo saw a reason to come up with some of his inmate's 'positive qualities', the lack of response to his presence would be on the list. As he doesn't see any possible reason why he'd do that, he just tilts his head to try to look at what book Envy's going through. He suspects he's not the best researcher, but trial and error is fine teacher if you don't want to ask for help.

Sanzo has never wanted to ask for help, at any point in his life.

He surveys the shelves around them with a more calculated approach. Well, his approach is generally just trying to read through everything he can find, but he's not bad at finding what books might have information which he wants.