Using the "Path" option it is currently not possible to load fonts with spaces in their name (or in folder names). Unfortunately there are a lot of fonts that have spaces in the file names.
(I'm using Lua(La)TeX.)

\documentclass{article}
\usepackage{fontspec}
\setmainfont{TT Norms Pro Serif-Regular.otf}[
  Path= ./fonts/
]
\begin{document}
hello
\end{document}