# blank page not created

I create a blank page using

\newcommand\blankpage{ %comando pagina vuota
\null
\thispagestyle{empty}%
\newpage}


Here it is one my page:

\thispagestyle{empty}

\null\vspace{\stretch{1}}
\begin{flushright}
\emph{Stay hungry, \\
stay foolish. \\}
\smallskip
Steve Jobs, Stanford University, 2005
\end{flushright}
\vspace{\stretch{5}}\null


Unfortunately adding \blankpage after that page, it doesn't work

-

Your \blankpage only contains one \newpage, i.e. the leading \null is put on the current page. It only works as expected if a page break occurred already direct beforehand. To make it always work you need to add a \newpage at the beginning. Should there be already be a page break, this \newpage will be ignored, so you don't get two extra pages.
\newcommand\blankpage{% comando pagina vuota