It is the 720p 31.5 diagonal screen if that helps
I assume you mean on the popup keyboard. It's in the bottom row next to the hyphen if it's the standard Roku keyboard. If it's the mini-keyboard that comes up when you try to search then there isn't one - try using a space which looks like an underscore with a little head and tail.
If it's one specific to a channel/app then there may be a way to switch the keyboard to symbols.