Compiling this example that uses EB Garamond font
\documentclass{article}
\RequirePackage{fontspec}
\setmainfont[Ligatures=TeX]{TeX Gyre Pagella}
\begin{document}
\fontspec{EB Garamond}[Ligatures=Historic,Scale=2]
Questo altere uniffatto fiato.
\end{document}
with XeLaTeX and LuaLaTeX gives two different results: the Q is shown with a long "swash" only in the PDF produced by XeLaTeX. Why?

luatex, you need to specifyContextuals=Alternate. See https://tex.stackexchange.com/a/133385 – Thérèse Oct 28 '16 at 17:07\setmainfont[Ligatures=TeX]{TeX Gyre Pagella}and substitute\setmainfont{EB Garamond}. Or use the\newfontfaceornewfontfamilycommands, which are more efficient than the\fontspeccommand. (There’s a question about that somewhere on the site.) – Thérèse Oct 28 '16 at 17:34