super and subscripts on stackrel variable

Something like this?

Note the use of \, (thinspace) to nudge the "f" superscript to the right, to improve its centering above the \omega character.

\documentclass{scrreprt}
\usepackage{amsmath}  % for \smash[t]{...} macro
\usepackage{scalerel} % for \stackrel macro
\begin{document}
$\smash[t]{\stackrel{\,\scaleto{f}{5pt}}{\omega}}^{(i)}_{kl}$
\end{document}

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Addendum to address the OP's follow-up question: Since the macro \lstmw will only be encountered in math mode, I'd define it as follows:

\newcommand{\lstmw}[3]{%
    \smash[t]{\stackrel{\scaleto{#2}{5pt}}{#1}}^{(i)}_{#3}}

and write $\lstmw{\omega}{\,f}{kl}$ in the body of the document.

In fact, to make the superscript term (here: f) look a little bit less skinny and brittle, I'd define the macro as follows:

\newcommand{\lstmw}[3]{%
    \smash[t]{\stackrel{\scaleto{\scriptscriptstyle #2}{5pt}}{#1}}^{(i)}_{#3}}

This "works" because TeX's math glyphs are optically sized, rather than just linearly scaled versions of the "standard size" glyphs.

The accentset command is another possibility. By default, the accent letter is in scriptscriptstyle, but you might be interested in having it in \scriptstyle:

\documentclass{scrreprt}

\usepackage{accents}

\begin{document}

$ \accentset{\mkern2mu\scriptstyle f}{\omega}^{(i)}_{kl}\qquad \accentset{\mkern1mu f}{\omega}^{(i)}_{kl}$

\end{document}