How can I view invalid characters in a file? How can I view invalid characters in a (text) file?

At the left is Notepad++ on a Windows machine. At the right is TextWrangler on a Mac machine. Notepad++ shows me what those invalid characters are, but TextWrangler just displays inverted question marks. How can I view those invalid characters (more meaningfully) on Mac?



OS: macOS High Sierra 10.13.3
Hardware: MacBook Pro Mid-2015
Sublime Text can display the invalid characters.