You want to compare glyphs between files? There is a tool called MergeGlyphs for that, and you can use one the Show Nect Font plug-in (in the Plugin Manager).
This isn’t something that’s entirely in the font. Depending on the shaping engine used you will get different results so what you see in Microsoft Word on Windows might not be the same as what you see on a Mac with CoreText or in Firefox or Chrome using harfbuzz. Anyway, there’s a Google tool, fontdiff, to do something like you show: https://github.com/googlei18n/fontdiff/releases
You can build from source or just use the binaries in releases. This doesn’t overlap like your example, but does show differences in shaping between two fonts. Here’s a good example showing differences: https://github.com/googlei18n/fontmake/issues/273
Oh, you said one is ASCII and the other is Unicode. Well, that makes it more difficult. Everything about those is different. They will have different input methods so you can’t use something like fontdiff. It sounds like you need something more customized.