I hope that this will get you going. In the following I have used the changepage
package to adjust the contents of a figure
environment depending on whether the figure ends up on an odd or even page.
% figpageprob.tex SE 509111 Is figure on even or odd page
\documentclass{book}
\usepackage{changepage}
\strictpagecheck
\usepackage{lipsum}
\begin{document}
\lipsum[1]
\begin{figure}
\checkoddpage
\ifoddpage
FIGURE ON ODD PAGE
\else
\raggedleft FIGURE ON EVEN PAGE
\fi
\caption{A figure}
\end{figure}
\lipsum[1]
\begin{figure}
\checkoddpage
\ifoddpage
FIGURE ON ODD PAGE
\else
\raggedleft FIGURE ON EVEN PAGE
\fi
\caption{A figure}
\end{figure}
\lipsum[1]
\begin{figure}
\checkoddpage
\ifoddpage
FIGURE ON ODD PAGE
\else
\raggedleft FIGURE ON EVEN PAGE
\fi
\caption{A figure}
\end{figure}
\lipsum[1]
\begin{figure}
\checkoddpage
\ifoddpage
FIGURE ON ODD PAGE
\else
\raggedleft FIGURE ON EVEN PAGE
\fi
\caption{A figure}
\end{figure}
\lipsum[1]
\begin{figure}
\checkoddpage
\ifoddpage
FIGURE ON ODD PAGE
\else
\raggedleft FIGURE ON EVEN PAGE
\fi
\caption{A figure}
\end{figure}
\lipsum[1]
\begin{figure}
\checkoddpage
\ifoddpage
FIGURE ON ODD PAGE
\else
\raggedleft FIGURE ON EVEN PAGE
\fi
\caption{A figure}
\end{figure}
\lipsum[1]
\begin{figure}
\checkoddpage
\ifoddpage
\raggedright FIGURE ON ODD PAGE
\else
\raggedleft FIGURE ON EVEN PAGE
\fi
\caption{A figure}
\end{figure}
\lipsum[1]
\end{document}
On the first run through all figure are assumed to be on even pages. On the second run through the figures know on which pages they are printed and their contents are adjusted accordingly.
The values that your document takes for the lefthand margin depend on the class you are using and any packages that affect the page layout. You can use the layouts
package to determine the margins if you don't know them otherwise.
You could define a macro along the lines of (less any typos and adding in extra bits):
\newlength{\mylength}
\newcommand*{\mymacro}{%
\checkoddpage
\ifoddpage
\setlength{\mylength}{<oddleftmargin>}
\else
\setlength{\mylength}{<evenleftmargin>}
\fi}
and use it like
\begin{figure}
\mymacro
% adjust the figure location by \mylength
%
\end{figure}
\dimexpr 1in+\hoffset+\oddsidemargin\relax
.