Creating a multi-level list numbered like 1a), 1b)

In this case you can easily create what you want using nested environments, you can use the enumerate environment for that, but in the inside one instead of use \item you can use \item[1 a)] for do it in a more explicit way. From your own MWE:

\documentclass[10pt, twocolumn]{article}
\begin{document}
\begin{enumerate}
    \item Something
    \begin{enumerate}
         \item[1 a)] apple
         \item[1 b)] pear
         \item[1 c)] banana
     \end{enumerate}
    \item Something more
    \begin{enumerate}
         \item[2 a)] watermelon
    \end{enumerate}
\end{enumerate}
\end{document}

Try the code above where you can see the nested environment I told you before. I don't know the environment inparaenum, so probably you forgot to load the package that defines it or you omit the code where you defined it in the preamble.

Anyway, you can also make your own style with the description environment or use the enumitem package. I'm almost sure that you can find here the answer, this seems not to be the first time I read the question.

[Edit I realised that using easylist is easier than enumitem:)]

I am assuming that you want to define an environment inparaenum that behaves like this. The easiest way to do this is (probably) using the easylist package:

\documentclass{article}
\usepackage[at]{easylist}% easy lists with @ starting each item

\begin{document}

\begin{easylist}
  \ListProperties(Style1*=\bfseries,Numbers2=l,Mark1={},Mark2={)},Indent2=1em)
  @ Something
  @@ apple
  @@ pear
  @@ banana
  @ Something
  @@ Frogs
\end{easylist}

\end{document}

This produces the list:

Another, more standard, alternative is to use the enumitem package:

\documentclass{article}
\usepackage{enumitem}

\newlist{inparaenum}{enumerate}{2}% allow two levels of nesting in an enumerate-like environment
\setlist[inparaenum]{nosep}% compact spacing for all nesting levels
\setlist[inparaenum,1]{label=\bfseries\arabic*.}% labels for top level
\setlist[inparaenum,2]{label=\arabic{inparaenumi}\emph{\alph*})}% labels for second level

\begin{document}

\begin{inparaenum}
  \item Something
  \begin{inparaenum}
    \item apple
    \item pear
    \item banana
  \end{inparaenum}
  \item Something
  \begin{inparaenum}
    \item Frogs
  \end{inparaenum}
\end{inparaenum}

\end{document}

This produces the expected list: