https://github.com/dbilyk/SymbolTextInspector/files/2496311/Symbol-Text-Inspector.sketchplugin.zip
Just select a symbol and hit Ctrl + Cmd + Opt + T or select Symbol Text Inspector from the plugin menu. If it has text overrides, you'll see a summary of all the text specifications that sketch exposes.
In some cases, the font is not found on your computer in which case you'll see an error for that text override in the list.
This plugin currently only inspects the first symbol in the selection, it will not display text overrides for multiple selected symbols.