Here you go, this is how a comic looks on the Nook:
I convert my comics with Calibre. I use the CLI in Linux to convert from CBZ to EPUB, like this:
ebook-convert The-Walking-Dead-70.cbr twd70.epub --no-default-epub-cover
This perfectly converts the file by trimming a little bit of the edges so that the resulting EPUB file will be better readable on the Nook Classic. I read the whole ”The Walking Dead” series on the Nook without a problem.