\documentclass{scrbook}
  %\usepackage{luatexja}
  \usepackage{fontspec}
  \usepackage{luatexja-fontspec}
  \usepackage[
    mode=text,
    detect-all,
]{siunitx}
  %\usepackage{luatexja-fontspec}
\makeatletter
%\typeout{\meaning\@begindocumenthook}
\begin{document}
  \ifdefined\gtfamily\gtfamily\fi Ω
  {\ExplSyntaxOn\makeatletter
   \ttfamily\meaning\@begindocumenthook}
  
  \SI{-2.5e-10}{mol.L^{-1}}\SI{1}{\micro\metre\angstrom\arcminute\arcsecond\ohm}
  \vrule\SI{}{\ohm}\vrule

 $\begin{array}{lSs}
%   \typeout{\meaning\@preamble}
   a&-.123 & J.mol^{-1} \\
   a&1.23e-3 & Hartree \\
  \end{array}$

\begin{tabular}{lSs}
%  \typeout{\meaning\@preamble}
  a&-.123 & J.mol^{-1} \\
  a&1.23e-3 & Hartree \\
\end{tabular}

\end{document}


LTJ
\d@llarbegin \__siunitx_table_collect_begin:Nn S{}\relax
\pltx@next@inhibitglue \ltjfakeboxbdd \ignorespaces
\@sharp \unskip \ltjfakeboxbdd \__siunitx_table_print:\relax \d@llarend

non-LTJ
\d@llarbegin \__siunitx_table_collect_begin:Nn S{}
\ignorespaces \@sharp \unskip \__siunitx_table_print:\relax \d@llarend
