How to find this unicode character U+202F in your LaTeX documents?

it is narrow no-break space so hard to spot but you can do

   \DeclareUnicodeCharacter{202F}{FIX ME!!!!}

If you want to just find it or

   \DeclareUnicodeCharacter{202F}{\,}

If you want to define it to something plausible.

If you insert the following code in the preamble (after loading inputenc), the text !!FIXME!! will appear wherever an undeclared unicode character occurred.

\makeatletter
  \def\UTFviii@defined#1{%
    \ifx#1\relax
      !!FIXME!!%
    \else
      \expandafte‌​r#1%
    \fi
  }
\makeatother

(Reference: This macro is defined in utf8.def. Run texdoc utf8ienc for the package documentation. Since the package could change in the future, this hack may also stop working in the future; so beware!)