Sometimes (e.g. in my Firefox browser) I see those Unicode fallback characters like the one below for the Unicode character U+0880 (just an example) instead of the real character.

Another example would be the character U+0CA0 which is used to represent the eyes in the famous "Unicode look of disapproval" (ಠ_ಠ ) emoticon, which needs the fonts-lohit-knda package installed to display correctly: The Unicode look of disapproval no longer displays correctly in 16.04 - how do I fix this?

I know this is because I miss a font containing this character, but how can I determine which font package I need to install to display a specific Unicode character correctly?